Round: 62 Ground: Hardcourt outdoor
| ITF Spain F31 | 2017/09/25 09:00 | Okagaki, Kosuke v Colas Sanchez, Alberto | 1-6,2-6 |
| Yokohama, Japan, Qualifying | 2018/02/24 03:55 | Garanganga, Takanyi v Kai, Naoto | 6-3,4-6,7-6 |
| ITF Japan F8 | 2017/06/10 05:00 | Goh, Steven v Kai, Naoto | 6-3,6-2 |
| ITF Japan F7 | 2017/06/06 01:00 | Shintaro Imai v Kai, Naoto | 6-1,6-2 |
| ITF Japan F6 Qual | 2017/05/27 01:00 | Furuta, Ibuki v Kai, Naoto | 6-2,6-0 |
| ITF Japan F4 | 2017/03/25 00:00 | Nakamura, Yuki v Kai, Naoto | 6-4,4-6,6-1 |
| ITF Japan F1 | 2017/03/04 03:30 | Furuta, Ibuki v Kai, Naoto | 6-2,6-0 |
| ITF Japan F7 | 2016/06/06 01:00 | Tanuma, Ryota v Kai, Naoto | 6-4,6-3 |
| ITF Japan F4 | 2016/03/26 00:00 | Kikuchi, Gengo v Kai, Naoto | 6-2,7-6 |