Stadium: Court 9 Round: 25 Ground: Hardcourt outdoor
| ITF M25 Tsukuba | 2023/03/27 00:30 | Seiya Nakanishi v Issei Okamura | 2-6,4-6 |
| ITF M25 Nottingham | 2023/05/01 09:00 | Issei Okamura v Ryan James Storrie | 3-6,3-6 |
| ITF M25 Nottingham Qual | 2023/04/30 09:00 | Issei Okamura v Joseph White | 6-0,6-2 |
| ITF M25 Nottingham | 2023/04/25 09:00 | Issei Okamura v George Houghton | 2-6,1-6 |
| ITF M25 Nottingham Qual | 2023/04/24 13:00 | Issei Okamura v Max Benaim | 6-4,6-4 |
| ITF M25 Kashiwa | 2023/04/06 03:40 | Kaito Uesugi v Issei Okamura | 6-1,6-4 |
| ITF M25 Kashiwa | 2023/04/05 05:35 | Issei Okamura v Sho Shimabukuro | 7-6,0-6,7-6 |
| ITF M25 Kashiwa | 2023/04/03 01:00 | Koki Matsuda v Issei Okamura | 1-6,2-6 |
| ITF M25 Kashiwa | 2023/04/02 00:30 | Taketo Takamisawa v Issei Okamura | 1-6,2-6 |
| ITF M15 Karuizawa | 2023/05/28 01:15 | Seiya Nakanishi v Yua Taka | 4-6,2-6 |
| ITF M25 Kashiwa | 2023/04/02 00:30 | Jeremy Jin v Seiya Nakanishi | 6-3,6-2 |
| ITF M25 Tsukuba | 2023/03/27 00:30 | Seiya Nakanishi v Issei Okamura | 2-6,4-6 |
| Challenger Yokohama | 2022/10/30 02:35 | Seiya Nakanishi v Daisuke Sumizawa | 3-6,0-6 |
| ITF M25 Sapporo | 2022/09/01 02:50 | Rio Noguchi v Seiya Nakanishi | 6-0,6-3 |