Tomiyasu joined Arsenal in 2021 from Bologna in a £19.8M deal. He initially established himself as a strong backup in the first team, but his career was impacted by injuries. As a result, he gradually fell out of favor with manager Mikel Arteta, who preferred younger talent.

Tomiyasu has spoken about his decision to leave the club, stating that it was a mutual agreement between himself and the team. He emphasized that his contract was not terminated unilaterally and that he did not unilaterally decide to leave.

According to Tomiyasu, the decision to leave was made amicably, and he is grateful for the support he received from the players, fans, and staff during his four-year tenure at the club. He acknowledged that he struggled with stress and anxiety during his time at Arsenal, particularly after playing only five minutes in the 2024-25 season.

Tomiyasu expressed his appreciation for the club's welcome and support during his time with Arsenal. He also mentioned that he was able to say goodbye to each player and staff member individually, which helped him feel loved and appreciated.