Van Wermeskerken started his career at Yatsugatake Hokuto at age eight, before joining Ventforet Kofu youth academy in 2008.
After several years in the Kofu youth system, van Wermeskerken was rewarded with a contract by Dordrecht in July 2013.
[2] On 9 July 2019, van Wermeskerken signed a two-year deal for Eredivisie side PEC Zwolle on a free transfer.
[4] On 27 October 2023, van Wermeskerken joined Eredivisie side NEC Nijmegen, signing a contract until the end of the 2023–24 season.
[6] On 14 March 2016, Sai received his first call-up to the Japan national under-23 football team for the friendly match against Mexico.