Life in Another World, Beginning with Thunder Breathing

Seventeen-year-old anime geek Du Yi is suddenly summoned to another world. Only after the fact does he realize that he has transmigrated into the world of RE:Zero. Then he discovers, to his shock, that he is living as Zenitsu Agatsuma from Demon Slayer, with a crystal-clear memory of all his techniques. Du Yi has never seen anything this intense. He panics at first, but he has gained Zenitsu's power and a stronger mind. On top of that, he already knows both anime inside out. This transmigration-and-possession plot is downright outrageous. Seeing the tragedy about to befall Emilia, Du Yi decides to take on Zenitsu's identity, explore his new powers step by step, and help the protagonist, Natsuki Subaru, set this world back on the right track. No System + protagonist grows stronger + Rem route + sweet moments and heartbreak + original story fused with the Rem IF route