In addition to his time at Komeito, he was also a top leader in Soka Gakkai, even reaching the position of Vice President at one point.

Going into the 1965 House of Councillors election, Tsuji's Komeito fielded 14 candidates under the slogan of "vote for the new party and the new people.

"[3] In a March 1966 Diet debate, Tsuji went somewhat against earlier Komeito policy in not advocating for the complete abolition of the US-Japan Security Treaty, instead supporting gradual abandonment of it.

[2] Although the party advocated for the immediate return of the Ryukyu Islands to Japan, Tsuji argued that sending the Japan Maritime Self-Defense Forces to the islands would be unconstitutional, instead advocating for the establishment of a subcommittee without the Budget Committee to handle the question of Ryukyuan defense.

After this, he returned his endeavours back over to Soka Gakkai, serving in a number of roles including vice president.