Im pretty sure I found the sauce!

• SauceNao SourceURL:https://danbooru.donmai.us/post/show/1345258
• Source:http://i1.pixiv.net/img03/img/lizhi880423/33018750.jpg
• SankakuId:1951782
• DanbooruId:1345258
• Similarity:96.84

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

• Title Romaji:Uchi no Ko no Tame Naraba, Ore wa Moshikashitara Maou mo Taoseru Kamo Shirenai.
• Title Native:If It’s for My Daughter, I’d Even Defeat a Demon Lord
• anilist Id:107956

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