"What's Mikumo got that I don't?"
"Well, to start with he's the protagonist."
(Actual answer: Tamakoma's secret sauce is a willingness to not just break convention - lots of people can do that - but to disregard convention's existence entirely. Lots of folks in Border could look at Chika's inability to fire at humans and figure out how to work around it, but Mikumo can just accept her skills for what they are instead of treating her like a limited sniper.)