There are a number of Resources to be found in Eiyuden Chronicle: Rising. Some of these Resources are obtained from various sources in the environment. This page will detail the location of the Ruby resource.
The Ruby is one of the gemstone resources, which you might find a few in chests throughout the game’s world. However, there are some spots where you can find the gemstones naturally, with the Ruby being a case. Unfortunately, there is only a single place where you can harvest Ruby in the wild, which will be in the Lava Ruins. Before heading straight there, note that you will need one thing in order to access the room with the Ruby, which is the ability to destroy Red Elementum Pillars.
Once you have access to the Fire Rune, head to the Lava Ruins and set out to either the Ancient Workshop or Charred Crossing signpost. No matter which you choose, your destination is the large room in between them, where you have a few choices for exits. Of course, the northeastern one is where the Charred Crossing signpost is, and the one you want is below that one. Break the Elementum Pillar in the way and progress into the next room. There will be a few enemies in the way, including an Armored Ogre. At the end of the room, though, will be the Ruby.
Trading for a Ruby
Once you have leveled the Trading Post on Second Street enough, you will also be able to trade for a Ruby. In order to do so, you will need two items, a Molten Crystal and a Lapis Lazuli. The Lapis Lazuli can be found on Snowpeak and actually has three different locations in that dungeon. For the Molten Crystal, though, you will need to fight enemies in the Lava Ruins, as the resource is the rare drop from any enemy there. If you are having trouble getting them, throw on some Rarity Pendants to increase the chance for them to drop.