You will be starting the Palace from the beginning, since you didn't get very far due to an authentication door earlier. Once you arrive in the Palace, pick your party, knowing that you can't use Haru yet because of story reasons, but that won't last too long. Also, you haven't started a Confidant with her yet, so her lack of abilities from that will be a bit of a hindrance. It's also a good idea to check your Personas and see if you can fuse any new ones, noting that you won't need a few of them now that you have some Confidants maxed.
When you're finally ready, take the initial elevator and return to the authentication door, being on the lookout for some Shadows and grabbing any treasures along the way. When you finally get to the door, Haru will open it and some scenes will happen, triggering a miniboss fight against Haru's Fiance. He will be accompanied by two Corporobo MDL-WKR robots and despite the way things are, this battle is fairly easy. You are forced to use Haru in the battle, which is a good thing, as Haru's Fiance is weak to Psy attacks and Haru has Psio herself.
Start the battle by attacking his weak spot, then use fire on the two smaller foes when you get a chance to initiate an All-Out Attack. Once the Corporobos are done (they might survive the AOA), you can chip away at the Fiance's health until you get another turn to strike at his weakness. After the battle is over and you get control back, look to your east to spot a chest that contains a Magic Ointment. Take the next elevator to come to a bigger area, where you see your final destination, somewhat.
There are two passages here, one going west and another east. Start by taking the western path, being mindful of the Shadow guarding a chest (Druid Amulet), and you'll find a Safe Room. That's all there is in this direction, so return to the previous area and go east this time. Eventually, you will come to a door, which is locked and can't be opened with Haru, so you'll have to find another way to unlock it. Luckily, there is a spot right next to you that you can climb, leading to a circular room.
Watching out for an enemy near where you drop in, make your way around until you drop on a beam. There will be some terminal controls and when you inspect it, Futaba will do her thing, opening some doors and obtaining a map of the Palace. Continue following the circular path to come to another vent you can crawl through, bringing you to the other side of that previously locked door (which is now open). Keep going forward, past what appears to be another elevator, and to another locked door. This one is different than the others, as it appears you need some kind of ID card. Double back to the elevator you passed and take it to the next floor, which is the Barracks.
There will be a short scene when you get off the elevator and your objective is to go into the room straight ahead. As you get close enough, you will eavesdrop and overhear some things. Do this with all four of them in the room to find out the Chief Clerk likes his sweets, so exit and go down the hallway you saw halfway. South will lead you to another locked door, while you will come to another Safe Room to the north. Exit and head north now, being careful of the Shadow with the red aura around it.
Note: There are two enemies in this Palace that repel physical attacks, Arahabaki (Awakened God) and Girimehkala (Rebellious Elephant).
Continue following the path as it goes north and you will find some different looking robots in small rooms. Your team suggests that you talk to them, although you will have to fight at least one in the end. If you remember from the workers, you know the Chief Clerk likes sweets, so if you want to test things out, go to the northern enemy and respond with "We're salesmen" and "We have sweets," which allows you to either fight them or run away. Of course, the northern one isn't the real Chief Clerk, so you can fight him if you wish to get the breakable object behind.
The bigger robot is called a Corporobo MDL-?, but they will be designated with a color (this one is red), as you will see why shortly. It is accompanied by two of the smaller robots you've already fought (weak to fire), while the larger one is weak to nuclear and electrical skills. A single All-Out Attack should be enough to finish them off, so it should be fairly easy experience. The real Chief Clerk you need to kill is located off to the east (can get a little more information that's not really needed by eavesdropping on the workers in the northern room along the way), netting you the Chief Clerk ID.
Defeating the Chief Clerk will trigger a shift change, with stronger enemies occupying the head honcho rooms. With the ID in hand, look for the locked door near the enemy you just took out and open it with the ID card, allowing you to progress further. In the very first room past the locked door is a chest with a Model Gun in it (used when turning a Persona into an item). If you look at your map, there is a room in the northeast corner, which is another worker room in which you can eavesdrop, as well as two more exclamation points.
These are the next round of head honchos (Section Chief) that you will need to eliminate for their ID card and just like the last bunch, only one of them is real. That one would be the northern of the two markers, where you will be fighting another Corporobo MDL-? (this one is blue) and three of the smaller workers. Those smaller ones are still weak to the same thing, but the bigger enemy is weak to wind this time. Defeat them all and you'll get the Section Chief ID this time. You can get to the next unexplored area by using the locked door in the southeast.
This is the final area in which you will need to guess what miniboss to defeat, with another series of workers to listen to, if you want. There is a marker in the southeast corner and another to the west, with your objective being the one to the west. This Corporobo MDL-? is green and actually looks different from the other two, but it is weak to both Psy and Curse attacks. It might survive an All-Out Attack, so be careful on a second round. Defeating the Chief Director will get you his ID, which means you are finished in this entire area. Head back to the safe room if you wish to save before continuing on.
Use the elevator in the southwest corner to return to the previous area, then you'll find another elevator past the locked door that opens with the Chief Director ID in the northeast. This will bring you to an open area, where you will find a lift that'll bring you across to another Safe Room, as well as a chest right next to it ( Rasetsu Ofuda ). Use your Third Eye to look for spots where you can jump across some platforms, being careful of the Shadows on them to avoid getting ambushed.
The path is fairly linear, with not much in the way of diversions. It will go southeast, then northeast and just before it gos back north/northwest, there will be a treasure chest with a Spyware-laden Gear inside. There will be a short conversation when you get towards the end, then you will find a door that leads into the next area.
When you first enter this area, you will see a ramp near you, as well as a path on the ground floor. Run up the ramp and cross some pipes to find a chest with a Black Kogatana inside. Return to the ground floor and follow the way below to another Safe Room. Enter the factory area to get a glimpse on how Okumura treats his employees, then it's time to dive into the meat of things. There will be a fork right away, with one way going north and the split heading west. If you go west right now, it will lead to a dead end with an interactive console that has a blinking blue light.
Note: You will start encountering Lilims in this area, which will prove useful for the next Strength Confidant fusion. Get one onto your team and that's all you have to do, since she already knows Masukunda as one of her default skills.
This is useless right now, but will become important very shortly, so return to the split and venture north this time. As you get closer to the door, a mechanical arm malfunctions and drops some boxes in your way, blocking your progress. Hmm, you will need to find another way around, so run back to that console you may have comre across before and access it. This console controls one of the robotic arms and you have the option to set it to 3x, 5x or 10x speed. It doesn't matter what speed you set it to, as the arm it controls will break and form a bridge for your bridge.
Head back to the northern path and cross the broken robotic arm, then continue to the north. Go into the "room" in the northeast, being mindful that there are two Shadows in close proximity here, so you might accidentally have to fight both back-to-back. Look for the arm console here and increase its speed to break it as before, forming another bridge. Find it and cross to find a locked chest ( Fury Blade , Bead and Emerald ) and another console. The arm that breaks this time will be in the northwest corner, leading you to the door into the next area.
From looking at your map, this area seems rather small, but it can be a bit confusing. The first thing you should do is go around and clear all of the Shadows that you can, as they will be a hindrance shortly. As you move around this area, you will see a short scene that shows off the hydraulic press. There is the purple one at the northern end of the room, as well as two blue ones in the western part. Look for the console on the northern end of the room, near the purple hydraulic press, which will let you enter one of three different values: Unpaid Overtime, Break or Lunch.
First and foremost, this console controls the blue presses, and Unpaid Overtime does nothing at all. Break will stop them for five seconds, while Lunch will stop them for thirty seconds, so you are going to want to choose the latter option. Of course, the one caveat is that the timer persists through battles, so you will want to heed the previous warning of clearing the Shadows. Once you choose Lunch, you want to start sprinting towards the two blue presses, opting to "jump" over the western of the two to find a treasure chest with a Fragmented Armor in it. Use the console here to jump back over the press and across the adjacent one, where you will see one last console. This is the one that will stop the purple press, allowing you to progress into the next area.
Go down the ramp and you will come to another Safe Room (there's a lot of those in this Palace). Exit and use the console near the base of the other ramp to create a bridge with the robotic arm. Cross the bridge and continue west, until you come to a bridge with a console and laser barrier. Your party will notice some smaller robots (of a different variety) on the other side, who seem a little ecstatic to be working for Okumura.
The nearby console stops the blue hydraulic press, which is near the entrance to this area, so you have quite a trek to get there. As soon as you pass over the bridge, jump over the gap at the northern platform shown on your map to find a locked chest ( No Mercy gun for Ann, Balm of Life , and Opal ). Return to the main area and head west, going to the northern end to find a console to bust another arm. This will let you get to the southern area, where you will find a treasure chest along the eastern edge ( Shield Goggles ).
The console nearby lets you stop the yellow hydraulic press in the northwest, letting you finally reach those workers, so heal up and approach them for battle. These Corporobo MDL-CH robots are not too tough, but they will use status debuffs (like Matarunda and Masukunda) on you. They are weak to ice, so if you have Mabufula (or another variant), use it to quickly knock them down; Yusuke is also a great substitute if you don't have him in your immediate party. Once you defeat the group, you find more will come. In fact, you will need to destroy a total of 15 robots before you're done here. Head through the door and up the elevator to reach the next area.
It looks like you'll be stepping out into space in this area...one small step for man. There's a Safe Room right next to you, so use that to save your game, then enter the western room to find a chest ( Parapsy Ring ). Approach the airlock with the blue ring and interact with it to move to the northern area. There's nothing else to do here, so take the elevator up to the next section, where you'll come across the first of two puzzle areas.
Go north and your party will point out that some airlocks are working, while others aren't (it will say "inactive" if it isn't working). There's only one way to go for now, so shoot yourself east and you will spot a switch on the wall. These switches, when you pull them, will activate one of the airlocks nearby while deactivating another. Ignore the switch for now and continue east, then flip the switch in this area, using the southern airlock on the east end. Be careful in these areas, as most are small and you won't have a lot of room to maneuver with the Shadows.
Note: There is a troublesome Shadow here, named Scathach (The Shadowed One), that has no weaknesses, so you'll need to resort to a critical if you wish to knock it down.
Hit the switch on the east end, then take the only airlock that works to the west to find another switch. Use this, double back to the south, hit the switch there again and use the airlock in the far west now. You should be back in the beginning area with the first switch you saw (and avoided), so flip it now and go west, then north to reach an elevator that'll take you to the second of the airlock puzzles. Before you do anything, you can use the Safe Room here to save your game, if you wish.
You only have one way to go for now, so head north, then east and navigate yourself to the southern end to continue east. This is where another mechanic will come into play, using an airlock will cause it to deactivate, while another will activate. There's still only one path for you to follow, so go north, east and then north again at the eastern end. Continue west twice and you will find a switch, so pull it and go south, then take the middle airlock to the north.
Head east, then north to finally get to a new area. Ignore the switch and keep going north, then south on the opposite end. Things might get a little confusing here, but you have two airlocks to use here in this room, one in the southwest and another heading north in the east. Use the latter, go north again and hit the switch here (northern room). Head south twice to a room with a chest ( Bead ), then west, south and west once more to the elevator.
There's not much to do here in the Weapon Production area, but there's a Safe Room to your east and a locked chest to the south of that ( Hero Eyepatch , Physical Ointment , and Magic Ointment ). Run into the northern room and you will spot the Treasure. You've finally reached the end of Okumura's Palace, so travel back to the entrance and enter the Velvet Room, as you should be able to finally advance the Strength Confidant by another rank.
Doing Some Fusion
Your next target for fusion is Hecatoncheires, who is level 42, with the twins requiring that you transfer Masukunda to it. There is two possible fusions you can do here and luckily, both of the Personas you can use know the required skill without any need to level them up. The first possible combination is Lilim and Unicorn, with Lilim being one of the enemies you can get from inside of Okumura's Palace (check the Export Line area). Unicorn, on the other hand, will need to be fused on your end (Isis + Kin-Ki, Clotho + Flauros, and Pisaca + Rakshasa are possible combinations).
Another Persona that has Masukunda naturally is Thoth, who was one in Futaba's Palace, as well as abundant in the Akzeriyyuth section of Mementos (towards the end). There are two Personas you can fuse with Thoth to get Hecatoncheires, either Sandman (more common since it was in Futaba's Palace) or Choronzon, the latter of which is common in the Kaitul area of Mementos. Either way, show the Hecatoncheires with Masukunda to the twins and you'll get your next order, a Bugs with Samarecarm, which you won't be able to do yet. Make sure you have a Fortune, Star and Tower Persona with you for Confidant visits in the upcoming week. You can finally return to the real world.