Probably after Chinese teacher Lin Shuhe integrated into that classroom as a student, he discovered that the little bastards he treated like his own sons had other unknown sides.
There is also a certain big Mensao who has been secretly in love with him for many years and suddenly unlocks some indescribable skills.
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A certain school bully: "Come on, come on, let me learn to curse from dad."
Lin Shuhe: "... Is it because there are too few homework assignments??"
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Nan Xun: "Shu He, please move into my house."
Lin Shuhe: "No, I recognize the bed."
Two days later
Lin Shuhe: "Get off my bed!"