Prince of Tennis: The Sixth Heaven Demon King

Bad News: Waking up in a different world. Good News: It's Prince of Tennis. Bad News: The protagonist was a tennis novice before the time travel. Good News: He met Jujiro, a demon who hadn't yet joined the U17 team. Furthermore, he awakened the mysterious Six Paths Dimension, where opponents he'd previously played against can appear in his dreams. Furthermore, each door in the Six Paths Dimension grants him a special ability bonus. After witnessing the rise of demons and facing off against the young "First Army," the protagonist joins Seigaku, completely overhauls the tennis club, and leads it to the national championship. He lays low in the U17 team, hones his skills in the expedition team, and rises to fame in the World Cup. Ultimately, he becomes the tennis king everyone dreams of! The synopsis is too much to read, but after the transition period, the excitement begins with the Jr. Tournament section. (Already available: the excellent Prince of Tennis fanfiction "In Prince of Tennis, I Have a Tennis Mini-Game...")