The team run a fish fry and invite the whole school. It's more like a service organization that a Battlefront, since they have no enemies.
Then Yuri stumbles in, badly injured. She blames Angel, but Tachibana's been there the whole time.
Who is the doppelganger then?
Tachibana had developed a skill to clone herself, but had failed to put any limit on the clones. She activated it in battle, and the clone of her was made with the will to fight. Then the clone made more clones.
Yuri hacks Tachibana's computer to change the skill to reabsorb.