Lymle can summon Big Fire Dog with Pink Bow at will for whatever, whenever she wants....
I never even so much as heard of the series Star Ocean, so I have no idea if that's any threatening at all.
Flandre's certainly the strongest psychotic Apocalypse Maiden (It's rather impossible to compete with the power to destroy all of existence. Flandre can do that with only her right palm), but it's questionable if she's the cutest, seeing as how Fanon depicts her.
Here's a video from the side of the Fanon that thinks that Flandre is just a misunderstood adorable little girl who was told to stay in a room for 495 years.
495 GO! Little Sister Emotion [Subbed]This right here is the reason why I say it's questionable if she's the cutest, since physically, she's only supposed to be like ten, or something.