User blog comment:Seieireppa/More info on Reverie for a Dying Star/@comment-26141862-20150731182635/@comment-1419424-20150731183343

Ostensibly, it's an absolute losing scenario. Will ends up as the last human on earth with no hope of victory, HOWEVER...

If you read To You, If You Might Find This, at that point it's a matter of pride for Will, specifically of human pride. He kept, and keeps, on fighting because it's his duty as a human, and also because he wants to leave that message for whoever or whatever comes after him (after humanity) that humanity once existed, fighting for what they believed in and never giving in. Through Will's existence and actions, he becomes that proof that humanity existed. He takes the entire burden of humanity onto himself as he goes out fighting.

And even then... don't you remember To You's ending...?

EDIT:  Shio will not figure into this story at all. At least, not as of yet. I have no plans for her, in other words.