The Anime Lad
Shin is reborn in a fantasy world and adopted by the hero Merlin Wolford. By fifteen, years of training have given him a remarkable amount of magical power. Merlin has not given him common sense. This leaves the adults with a teenager who is prepared for magical danger and poorly prepared for ordinary society, an oversight with predictable administrative consequences.
Super Eyepatch Fox
Raised in seclusion by the renowned Merlin, Shin reaches fifteen with extraordinary magical skill and little idea how ordinary society works. He enters an academy where even routine demonstrations reveal that his standards are wildly distorted. School life gives the overpowered student classmates and social rules, neither of which can be solved by adding more force.
Gigguku
Shin has spent his new life learning magic from a legendary hero, but nobody remembered the common-sense lessons. That gap is the whole delicious engine! At fifteen he has enormous power and no reliable idea how ordinary people operate. Every social expectation threatens to become a new kind of test, while his lack of calibration keeps the power fantasy from feeling smug.
Father's Basement
The protagonist receives elite training and overwhelming power before school starts, removing most conventional suspense. Shin is at least entertainingly unaware of the imbalance. Raised by a famous magician away from society, he enters an academy with no reliable sense of what counts as normal magic or behavior. The comedy earns more than the combat because classmates can challenge his judgment even when nothing challenges his output.