I recommend 'The Star of the Net King' and 'The Stage of the World of the Prince of Tennis'. Both books were Doujinshi novels about the tennis prince. The female protagonist had to travel to the world of the tennis prince and have a love story with the male protagonists such as Echizen Ryuuma or Tezuka Kunihiro. The former had the female protagonist Bai Tian as the main character, while the latter had the Japanese representative team led by the samurai Echizen Ryoma fighting in the World Competition as the main plot. I hope you like my recommendation.