You need to beat the character in campaign mode to unlock, in any difficulty.
Jotaku, Anime Game Gamer
I. Eternal Return NA Immortal Tier
II. Super Mecha Champions NA Legendary Tier
III. Tokyo Ghoul: re Call to Exist NA Top #2
IV. Fate/EXTELLA Link: NA Top #9
V. Senran Kagura PEACH BEACH SPLASH: NA Top #3
I. Eternal Return NA Immortal Tier
II. Super Mecha Champions NA Legendary Tier
III. Tokyo Ghoul: re Call to Exist NA Top #2
IV. Fate/EXTELLA Link: NA Top #9
V. Senran Kagura PEACH BEACH SPLASH: NA Top #3