[2] In 1999, due to economic downturn caused by the Lost Decades, his father's restaurant in Osaka closed and he returned to Spain, leaving Saito with a single-parent household.

After observing his mother's hardships as a single parent amidst Japan's economic stagnation, Saito decided to pursue a career in politics.

[5] On April of the same year, Saito began serving as a secretary to House of Representatives member Seiji Maehara.

In October 2018, the Democratic Party for the People announced that it would field Saito as a candidate in a constituency in Kyoto Prefecture for the 2019 Japanese House of Councillors election.

[10][11][12] In October 2024, it was announced that he had joined Nippon Ishin no Kai and would stand for the party in the 2024 election in the Shiga 1st district.