Was Carried by the Mother-in-law of the Saint to Break into the Collapse!

Kiana, Kiana, what did I do to make you disrespect me so much?I know that you became a Valkyrie in Jidong, your strength improved quickly, you lived a good life, you have teachers and close friends who care about you, you don't need my past... But now you come to me and say: "Say Miss Celia, get out of this room." You have no respect for me at all, you don't treat me as a family member, and you don't even want to call me mom.
—Stop talking nonsense and get off my boyfriend's bed.
No.
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The above is a nonsense version of the introduction, seriously.
This is the story of a ruthless and cynical middle school boy who is transformed into a hero by a gentle and beautiful big sister.