An alchemist in sengoku era (A demon slayer AU story)
A boy schoolboy died in an accident, and find himself reborn in medieval era of alternate earth, where supernatural existed, he reborn as prince of england, Henry Tudor, a great alchemist in court. He made a terrible mistake yet was never blamed by people, as both royal and civilian claimed it to be minor error in handling supernatural, even church turn blind eye to it. But to Henry this is worse that being hated, for being loved despite his blunder, he wanted to be punished for his action, yet people motivate him to move forward, distraught he went on self imposed exile as he believed that don't deserved to be called and englishman or english royal.
He reached Japan, where he decided to live his rest of his life in atonement, he originally planned to abandon alchemy, once and for all, but in the sengoku era of Japan, he couldn't watch people suffering from wars, dieseases and famines, so he decided to continue his alchemy practice, to help people, one day, during his usual work as an alchemist aka foreign scholar by Japanese people, he befriended Yorichii, not knowing he will become an important figure, afterward his friendship with strongest demon slayer.