| 10/23/2014 |
Drafted by the Hokkaido Nippon-Ham Fighters in the 1st round of the 2014 NPB Draft from Waseda Uni. |
| 12/26/2020 |
Signed as a Free Agent with the Texas Rangers. |
| 05/21/2022 |
Round Rock Express placed RHP Kohei Arihara on the 7-day injured list. [Auto] |
| 05/31/2022 |
Round Rock Express activated RHP Kohei Arihara from the 7-day injured list. [Auto] |
| 08/16/2022 |
Texas Rangers selected the contract of RHP Kohei Arihara from Round Rock Express. [Auto] |
| 09/11/2022 |
Texas Rangers designated RHP Kohei Arihara for assignment. [Auto] |
| 09/14/2022 |
Texas Rangers sent RHP Kohei Arihara outright to Round Rock Express. [Auto] |
| 01/01/2023 |
OSA scouting updated ratings (potential): Stuff: 40 (40); Movement: 45 (45); Control: 55 (55). |
| 07/09/2023 |
Was selected to the 2023 Pacific Coast League All-Star Game. |
| 01/01/2024 |
OSA scouting updated ratings (potential): Stuff: 45 (45); Movement: 45 (45); Control: 60 (60). |
| 01/01/2025 |
OSA scouting updated ratings (potential): Stuff: 45 (45); Movement: 45 (45); Control: 60 (60). |
| 05/23/2025 |
Injured (mild hamstring strain),day-to-day for 3 days. |
| 06/15/2025 |
Injured (mild hamstring strain),day-to-day for 2 days. |
| 10/11/2025 |
Wins the 2025 Pacific Coast League Round 1 with the Round Rock Express! |
| 10/24/2025 |
Wins the 2025 PCL Outstanding Pitcher Award. |
| 11/11/2025 |
Signed a 1-year minor league contract extension with the Texas Rangers organization. |
| 01/01/2026 |
OSA scouting updated ratings (potential): Stuff: 45 (45); Movement: 50 (50); Control: 60 (60). |
| 04/24/2026 |
Injured (mild abdominal strain),day-to-day for 5 days. |
| 07/01/2026 |
Injured (sore ankle),day-to-day for 2 days. |
| 07/17/2026 |
Injured (biceps strain),day-to-day for 3 weeks. |
| 10/10/2026 |
Wins the 2026 Pacific Coast League Round 1 with the Round Rock Express! |
| 11/28/2026 |
Became a minor league free agent. |
| 01/01/2027 |
OSA scouting updated ratings (potential): Stuff: 45 (45); Movement: 45 (45); Control: 60 (60). |