Tsuna-Sensei from a Parallel World

In this world, Tsunayoshi never met his teacher and never became the Tenth Vongola Boss. He lived an ordinary life, and because his grades were poor as a boy, he became a wage worker soon after graduating from middle school. Then a System suddenly found him and sent him to various worlds to work as a teacher, educating students and completing missions. Tsunayoshi: With the knowledge I have, I can become a teacher and teach others? System: Of course! The System said the students he had to teach were all problem children, each an elite. He didn't need to teach them any academic knowledge, only help them embrace the fine qualities of kindness, truth, and beauty, and let go of their hostility. Tsunayoshi: ?? Tsunayoshi tried his hardest to refuse, but the System forcibly transported him to other worlds. Unable to fight back, he could only complete the missions as quickly as possible and go home. From then on, Tsunayoshi used his wits to deal with all kinds of troublemakers. There were vampire nobles who resorted to violence at the slightest disagreement, cold and twisted families, and certain mafia members with off-the-charts intelligence. Even amid all this danger, he also found moments of warmth, like the secret concern of a certain fox and the delicious cooking of a sunny girl. Tsunayoshi gradually honed his strength and steeled his resolve, cherishing everything he had in the present, for better or worse. When he completed all his missions and returned to his own world, he thought he could finally live peacefully with his mother. But then a certain man showed up, claiming Tsunayoshi had the blood of a certain family and that he had come to teach him to become an excellent boss. Tsunayoshi: ?? Do you even know what my job is? R: ?? This isn't what the file said! Upcoming story: The Day I Got the Reversal System One day, Minamoto Chigusa suddenly gained an ability: the Reversal System. It could reverse anything. As soon as he gained the ability, he heard a voice from the heavens. "How far will you take this ability?" Obviously, he'd do good deeds and bring peace to the world, Minamoto Chigusa thought. Turn Geto's cursed spirit orbs into delicious treats: Thank you so much. Reverse Dazai and Chuuya's relationship: turn them from mutually loathing partners into close friends who adore each other. Reverse the little Shinigami's nature and give him an angelic disposition: let everyone get along harmoniously wherever he goes. Reverse the negative emotions of cursed spirits into positive emotions: make the world a better place! Minamoto Chigusa thought happily, "This ability is great. Everyone must be so happy." The people he'd harmed didn't agree. Dazai: Why do you mess with me the most? I don't want to have my personality reversed into an obsessive workaholic like Kunikida, and I don't want to be friends with Slug either! Chuuya: Being friends with Mackerel is disgusting. 5t5: I'm going to become a gentle mother figure? The perennial elementary schooler: Does this mean I really do have a Shinigami constitution? "Hey, you're just playing with us, aren't you?" the victims said dangerously. Minamoto Chigusa, watching the show: Smiles don't disappear, they just move elsewhere. Even if you've lost your happiness, there are more smiles on everyone's faces now. Theme: A good teacher guides students onto the path of light