Easy Loyalty
To gain easy loyalty with your characters, simply go to Challenge mode and find a VS match to play. Once you start, hit Start and choose the Give Up option. Do this three times and you will lose the match. There is no downside to this, but your loyalty with that character will go up.
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Secret Character - Mizuki
Sometimes while playing as Mizuho, it will automatically switch to her twin sister (Mizuki). Mizuki has a completely different personality from Mizuho - it is sometimes interpreted as Mizuho having a split personality. That is not the case, she just has an alternate hidden character.