 If you liked
Blassreiter
|
 ...then you might like
Towa no Quon 1: Utakata no Kaben
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Both have a main character who has a special power that has them transform into a super powered humanoid being. Both main characters focus on saving those with special powers like their own.
Both involve people transforming, attcking people and being targeted by an organization that deals with their disposal. Both have people that can control their power and people who can't. One difference is in Blassreiter, it's infectious but in Towa no Quon, they are born that way.