But still something wrong with that bird though, Idk why a MC would have something like that (Story wise (as in the game))
Would make more sense if the abilities for the dark one to be able to brainwash and the light one to neglect that effect (Game Wise)
Based on what Cecil and Bertia thought earlier in the story, it's not really brainwashing ability. It's more to a misuse of existing ability, like how many isekai characters got their cheat skill out of "junk skills" by combining and using it outside what's written in the manual.
The light element heal, and provide comfort (in RPG, that is probably something like increasing morale, or healing mental abnormal status such as panic, confusion, etc).
But when used in normal situation and in prolonged period, it can become addictive as being separated from it caused a feeling of loss (being suddenly dragged out of a comfort zone)