[4] Kasai represented Japan at the 2020 Winter Youth Olympics, where she ranked 9th in the girls' individual Nordic combined event.

[5] In December 2021, Kasai won the women's championship at the Nordic Ski Yoshida Cup Jump Tournament.

[7][3] At the 2021–22 FIS Nordic Combined World Cup Kasai ranked second in her two competitions.

[11] At the 2023 Winter World University Games in Lake Placid, Kasai medaled gold in the women's individual Nordic combined event and silver in the mass start event behind her sister.

In the 2022–23 FIS Nordic Combined World Cup, Kasai ranked seventh overall.