If we're doing cliches, go all out! Our ditzy heroine is a total novice, who (somehow) has a crazy hidden power potential that can lay waste to entire battalions.
Black-haired Ace-Oneesan (yes, I named her) has a TRAGIC backstory, with her entire family/former lover/both killed in an ironic manner. Her flirty behavior is just a cover for her broken heart and broken mind that only the true love of Heroine-chan can heal. Also, she's a cyborg who'd self-conscious about her body modification, but Heroine-chan is into that.
But then loud Rival-san appears and tries to also aim for Heroine-chan's affection, Heroine-chan is torn and asks shy and quiet ChildhoodFriend-chan for advice, who tells her she should listen to what her heart tells her, even though she herself doesn't do so and is left with a broken heart, because in truth she has also loved Heroine-chan for a long time now, but she never confessed, because she didn't want their relationship to change and because they're both girls and it could never happen....poor ChildhoodFriend-chan TToTT
The villains is defeated with the power of love and the befriended