Team Leader: Usui because he's one of the only anime guys that could legitimately build a harem.
Brawler: Koneko because she's just insanely tank and cute.
Weapons Expert: Noel because
she restored 'The Silent Reaper' that kills hundreds of thousands of people
Brains: Yuki, what can be smarter than the Data Integration Thought Entity?
Medic: Vanilla, through her belief she heals just about anything.
Speed Fighter: Sen because she fucks shit up.
Mascot: Self explanatory.
Guy who dies first: Pfft, i still have no idea why all the girls in IS love him.