[renowner]

I mean. . .Dagger buffs damage for 10% Max hp every turn. Dullahan's rage drains 10% hp every turn. Ki Awoken drains hp every turn. There's not really any berserk, super mode buff that doesn't have drawbacks every turn. So just granting yourself more health would still need to have some pretty hefty drawbacks associated with it aside from 'hey you just lose some health eventually if the status ends.'

And just gaining more health to take more damage seems bad.
Lowering your hit doesn't seem fun.
Lowering your evade seems imbalanced for something that already just makes you tankier. Nothing in the game as far as I know just raises your health while also healing that newly obtained health, which on its own could open the door to even more disgusting ghost stuff.