Complete all 8 Tournaments, then complete any Tournament with your preferred character to unlock their Ending.

Ending	How to unlock
Adjo Ending	After finishing all 8 Tournaments, complete any Tournament as Adjo.
Dragov Ending	After finishing all 8 Tournaments, complete any Tournament as Dragov.
Finn Ending	After finishing all 8 Tournaments, complete any Tournament as Finn.
Killen Ending	After finishing all 8 Tournaments, complete any Tournament as Killen.
Kuro Ending	After finishing all 8 Tournaments, complete any Tournament as Kuro.
Nemo Ending	After finishing all 8 Tournaments, complete any Tournament as Nemo.
Renwick Ending	After finishing all 8 Tournaments, complete any Tournament as Renwick.
Seager Ending	After finishing all 8 Tournaments, complete any Tournament as Seager.