Read this yesterday, but had not the time to post anything. I did want to huddle in the corner with my arms around my knees while rocking back and forth humming afterwards ... I somehow missed the Yasumi-centric mention in your original post, so I spent a bit trying to figure out whose perspective this was from (which worked well for this piece).
QuoteI could have a slight bias there, though. I mean, she loves him, so I do, too.
Hmm. Sounds somewhat like Koizumi...
QuoteI could vouch that she's right about it, even if she doesn't even know it.
More evidence that its Koizumi...
But then:
Quotesince I was made just for a purpose
QuoteSo even if I was made for a purpose, I had some extra perks
Perhaps Nagato?
QuoteSo even if I am a tool made for a job, I can do more.... I wonder if I was really the best designed tool for the job, though. What good does being in love do me? I'd be doing what I was made for regardless of my feelings, wouldn't I?
OK. definitely Nagato.
Then the next paragraph blew that out of the water.
Keep reading, then:
QuoteThis makes that sempai
Sounds like Kanae from ... Oh! Yasumi! Keep reading to make sure... (further quotes confirm this supposition).
If that was intended (even if not), well played.
I like the introspection taking place. I got a feeling of isolation - she knows all but is powerless to do anything outside her purpose. That existence would be quite frustrating:
QuoteHe's like me, though, and doesn't really have those choices, though he at least gets to think he does.
Ignorance is bliss in this case.
Some typos:
QuoteHow often can someone know that they love someone?
I missed this the first couple of read-throughs (I read these types of stories several times hoping to find an "out" for the protagonist), but is often the word you want here? Are you looking for a concept more like assuredness or confidence?
QuoteThere's an infinity of things that never even get that after all!
I like this from a poetic license point of view and reads well, so maybe leave it as is, but it should be "an infinite number of things."
Quotefull of unknown surprised
Surprises?
QuoteThe only exceptions were things that would make her happy, or save that sempai some trouble, and those things weren't allowed to utilize the power
I think this sentence would read better with dashes instead of commas. I stumbled though this each time I read it.