The Legend of Heroes: Trails of Cold Steel II - New Game+ Hidden Scene

Accessible in New Game+. You must have collected the Black Records and have given them to Thomas before proceeding to Karel Imperial Villa. At the start of the Epilogue, don't forget to talk to Thomas to get the deciphered records. At the start of the final day, Thomas and Rosine are nowhere to be found but once the Reverie Corridor appears, they would be in the rooftop, approach them and watch the scene.
Location for Black Records
Black Records 2 - center merchant at grand market when you first enter Celdic
3 - after you finished the hidden quest St. Veronica's tears, go back to the sewers where you fought the boss
1 - atter you recruited Clara, go back to where you fought the big spider
4 - given by Norton after the quest Gone Air
5 - second visit to Lohengrin Castle, south western of the first area of the castle

https://kiseki.fandom.com/wiki/Black_...

If you want to know more what the hell is he talking about, play the Liberl and Crossbell games. Loads of information about the lore, Ouroboros, Church, Dominions and artifacts are in those games.