After you regain control of Yuna on the Celsius, immediately begin by speaking with Rikku, and do so quickly: the event is apparently timed, and it’s needed for 100%. After doing so, talk with Brother, Buddy, and Paine each several times until you get repeats of earlier text. Speak with Shinra next, and finally Rikku to trigger a scene. Afterwards, speak with Tobli and choose “ On with the show! “
Once the concert is over and done with, head to the Bridge. Speak with Maechen and don’t interrupt what he says at all, but listen to the whole thing. Head to the Engine Room next to find Leblanc; talk with her to get the Crimson Sphere 5 . Go back to the Bridge afterwards and talk to Shinra to end the mission, and to end the Chapter. Just one more to go!