Im pretty sure I found the sauce!
Found On Trace.Moe with a similarity of 0.78: - Title English:If It's for My Daughter, I'd Even Defeat a Demon Lord
Asside from being in a schoolgirl outfit, i cant find any evidence that they are underaged, its not drawn in an underaged manor, and its not from any underaged anime character i can find. Original reported not responding, so im resolving for now, if they get back to me ill revisit