Arguably, Ambassador Colias Palaeno from Investigations, who manages to really grow on a lot of players, and who shows up with a small army near the end and pressures the Big Bad into staying put with thinly veiled threats. And he keeps smiling while doing it.
We have Rena, whose primary prerogative on a normal day is to find cute things to take home. When pushed to protect herself or her friends, she can non-fatally swing around a cleaver like no one else.
Satoko, appropriately dubbed 'The Trap Master' by the rest of the cast, is somewhere between 9 and 12 years old and very frequently The Woobie, yet she can trap, confuse or outright take out trained, fully grown men with minimal effort on her part.
Finally, we have Hanyuu, a little girl around Rika's age, cute enough to be kidnapped by Rena three times in two minutes, who is also Oyashiro-sama, a Physical God who is promoted from The Voice to a full cast member during the final arc.
Veridadia from Yumina The Ethereal, who can turn herself into a BFS capable of destroying anything in a single strike.
Rosemary from Rose of Winter is this in spades. She's a hopeless romantic, flusters easily, thinks "this is a bit of a pickle" is coarse language, and wants to be a knight not for the thrill of battle, but because she sees it as a way to help people. Which she does by swinging a sword that would make Cloud Strife jealous at any and all gigantic wild animals that try to harm the prince she's sworn to protect.