I feel like the second person perspective is supposed to drive home the point of how fleeting our lives are. The story is about a mayfly like you and I facing eternity, not about eternity facing us. If you want a story like that, go read To You, The Immortal a.k.a. Fumetsu no Anata e.kinda lazy, it's a fun concept but we have a billion year old person and the story is told through the eyes of a boy that fancies her?