Hibiki may be S rank (or just S), but than there is Inazuma....

Plasma-chan defeats all, when motivated.

She did one-shot Sendai after learning Sendai plundered the warehouse food.

Lambchopocalypse said:

She did one-shot Sendai after learning Sendai plundered the warehouse food.

Considering she one shot Sendai who's an S-rank in her own right, I say Plasma-chan is somewhere far above that. <.<

Inazuma seems like a wildcard. shes probably low A rank most times, but push her buttons, and she becomes the strongest S rank. makes sense since shes beats just about everyone except maybe Reiji in terms of combat experience.