[agetreme]

I like to keep things simple so this may sounds like Troll-logic:

Esper ability is related to Personal Reality which delve deep inside a person's brain. It is probably part of their sub-conscious which define who and what they are (in a way similar to Magician's Sorcery Name which was craved into their soul).

Remember: Personality does not change the power, it only influence how the power is being use. So even with multiple Personality disorder, there is only one sub-concious Self functioning as the fundamental baseline which define an Esper's ability.

=

I know it is bad which is why I need to check the following analogy for Idol Theory:

Spoiler for Analogy:

Magician: Imagine a Master Craftman who know how to make a powerful sword that deal 999 000 damages. When the Master Craftman died, he only leave behind a couple of clues for his apprentice to figure out how to make the sword.

Through multiple Trial and Error, the Apprentice managed to make a similar sword. An imperfect copy that can only deal 999 damages.

Although it was not as powerful as the original.... it is still relatively powerful.

A Magician can grow stronger by trying to make the replica as close to the original as possible. In doing so, learn how the original work and try to replicate the result as reliably as possible.

Spoiler for Yumene's power:

Unrelated side note: Changing Yumene's power name to Euphoria. The description of her power remain mostly the same... It make people happy by bringing out their dream and desire. The over-simulation causes the brain to....hallucinate.

In more layman term: Her power technically make people high as if they are taking drugs.

Hence the hallucination effect.

Edit:
I think I will leave Kosuke aside make another Protagonist, Yusuke.

Reason being:
Kosuke is so normal that he is boring and I need somebody closely related the story's theme.

Yusuke is Akihisa's (baka-test) level of stupid (mostly because he operate on logic which doesn't make sense) and his power force people to daydream.

Seems like an useless ability but.... His power is technically dream manipulation. Guess what is his level 4 ability.