You know you're spending way too much time on Danbooru, when you can reliably identify a LOT of Touhou artists by the thumbnails alone. This one was no exception.
ezekill said: And that M4 looks like an M16 (is that RIS real?) kitted hard.
M4s and M16s don't get modded that much. I'd still say it's an AR-15. Civil ownership of one allows you to do anything to your rifle as long as it isn't illegal and that handguard and stock don't look cleared for military use.
I do believe that Sakuya does look good with an SBR, PDW, or SMG. Gotta need that maneuverability in the SDM. Suppressors would be needed to keep quiet in the library as well.
M4s and M16s don't get modded that much. I'd still say it's an AR-15. Civil ownership of one allows you to do anything to your rifle as long as it isn't illegal and that handguard and stock don't look cleared for military use.
While you're right that that's an AR-15 (look at the selector), that exact kit actually is cleared for Special Forces and the Rangers... if the soldier is willing to jump through the regulatory hoops to get their orders changed accordingly.