About Shun...*spoiler*

[DarkMaster]

all the routes have pretty happy endings.
yes you could say his new way of life (vague to avoid spoilers) is hard one, but he always have someone there with him.
and he always comment how his choice was the right one.

[iamin7ove]

so even Lesteena can find happiness in her ending ?

[Mane]

That one is for you to decide...I personally thought Lesteena's route was the most bitter-sweet of the lot. And yes, Yuuto comments that he would never regret his choice.

[iamin7ove]

Ideals...hmm ?
Man, i hate that crap...
Its not wrong but its sad.

Usuallly i can wish for them to be together next life but it seems that Yuuto is not even going to have a next life

[KyouSama]

The way an ETERNAL to be forgotten by humans are by leaving the world they're currently in.
And the way a HUMAN to be forgotten by other humans are by passing the "gate" to the labyrinth of time, which resides the high-rank eternity swords.
Since shun didn't pass the "gate" to become an eternal, and he hadn't left the world, he still exist in human's memory.

[iamin7ove]

Mah but basically he wont reappear even if the world rewrite the history (Kyouko and Kouin does even after they are dead)