My initial thought after reading it the first time was that
// I’m trying to think of who this is speaking… At first thought, Gil and Pani come to mind because of the use of “so I was useful…”. However, I somehow feel that the sense of “controlling the aurora” goes a bit deeper here. ~Gnash
// Maybe it’s Kagari after giving Sakuya back enough aurora to return once more? To be part of his family for a while longer before heading off to his last fight? Idunno… Fun to think about anyway. ~Gnash
Since then, I pretty much think of it as
Since most of the routes in Rewrite take place in the “alternate timelines” explored in Moon, I think this was merely Kagari looking at a possibility, seeing happiness and life in one of those brief moments, and allowing it to continue. The thing to remember is that this whole speech takes place in this timeless transition to the Moon, where time is irrelevant, and all versions of Sakuya converge. I think of it as this one moment of absolute clarity for Sakuya, who fought so hard before the last Salvation, and has been working to repent for his failure the entirety of this cycle. He sees all that he has accomplished, all that can be accomplished, and is able to have a few words with the being who is making that possible. Idunno, it’s a thought anyway.