The Days I Became the Demon King at Rikkai

At Rikkai, there's the Child of God and the Emperor. There's also a military strategist, a gentleman, and all sorts of animals. And one seaweed head. But the most famous and fearsome of them all is the Demon King himself, Xie Anbo. They say everyone at Rikkai has been tormented by the Demon King. They say the Demon King has a weapon at his side that makes people wish they were dead. They even say the Child of God has fallen victim to the Demon King's ruthless hand. Xie Anbo: Who started these rumors? Child of God: Hee hee. Fox: Hee hee. Piglet: Hee hee. Gentleman: Hee hee. Emperor, Strategist, Brazilian Wolf, and Seaweed Head: Hee... hee? Reader's guide: 1. The characters' personalities will be altered a second time. If that bothers you, don't read. +++++++++++++++++++++2. Rikkai will win three consecutive championships. If that bothers you, don't read. ++++++++++++++++++++3. There are quite a few original settings. If that bothers you, don't read. ++++++++++++++++++++4. This is a crossover. Characters from other anime may make occasional appearances, but the main plot is still about tennis. ++++++++++++++++++++5. Seigaku will be crushed. If that bothers you, don't read. (I'm not a Seigaku hater, but they will be thoroughly crushed.) ++++++++++++++++++++6. The King of Rikkai has no weak spots! My new fanfic project is up for pre-order. Please add it to your favorites: [Shenhe, Are You Laying Eggs or Bearing Fruit?] On the first day an ordinary human boy named Jiuhua arrives in Teyvat, he is surrounded and attacked by a group of Hilichurls. Luckily, he's tough enough to make it through, and manages to wipe them out using one of Teyvat's rules. Then a shorty (crossed out) suddenly drops from the sky, calling himself the Conqueror of Demons and saying he's here to take care of the monsters. Jiuhua: If only you'd arrived fifteen minutes earlier... You could've been the hero who saved the beauty! QwQ Xiao: ...Beauty? Jiuhua has lost all his memories and remembers only his name. He has no idea how he ended up here, until someone points him in the right direction and he follows his instincts to search for his memories. "A returner comes back to save the day." Jiuhua doesn't know what a returner is, and doesn't care who the term refers to. He only wants his memories back. Nothing else has anything to do with him. From the day he arrived in Teyvat, one fierce desire has burned in his heart: to go home! He has to go home! No one can stop him from going home! But where is his home? At first, Jiuhua thinks his home is in another world. But as more and more memories return, he realizes his identity is far from simple! Because he isn't even human anymore! Xiao: Not being human is pretty good. Jiuhua: What's so good about that? QwQ Xiao: It means you can stay with me for a very, very long time. Oh no! He's falling for him! Theme: Unrelenting effort is the best way to open doors