[1][2][3] On November 1, 2019, Tominaga made his collegiate debut for Ranger College, against Missouri State University–West Plains, scoring 19 points in a 100–84 win.

[4] On November 28, Tominaga verbally committed to play for NCAA Division I program Nebraska, under former NBA coach Fred Hoiberg for the 2021 class.

[1][11] With Tominaga playing for Ranger College, the team finished the season with a 28–3 record, helping them clinch a position in the NJCAA national tournament.

[16] For his performance, Tominaga was named Northern Texas Junior College Athletic Conference Player of the Week for February 28 to March 6.

[15] On April 22, Tominaga posted a game-high 25 points, sinking five 3-pointers in an 87–83 win against South Plains College, sending the Rangers to the Final Four round of the NJCAA Division I Championship.

He made his debut for Nebraska on November 9, 2021, against Western Illinois, finishing with three points, one rebound and three steals across 18 minutes of play in a 75–74 loss.

Among Big Ten players, his average of 20.3 points per game from February 1, 2023, to the end of the season trailed only Zach Edey and Trayce Jackson-Davis.

[33] After initially entering his name into the 2023 NBA draft, on May 31, 2023, Tominaga announced his withdrawal and intent to return to Nebraska for his senior season.

[37] Tominaga made his international debut when he was selected to be a part of the Japanese squad that competed at the 2018 FIBA Under-16 Asian Championship, where he led the team in efficiency (13.3) and points (17.5) per game.

[43] Tominaga earned his first senior national team call up after being named to the 12-man roster that represented Japan for the third window of the 2023 FIBA Basketball World Cup Asian Qualifiers held in Australia.

His father, Hiroyuki, was a 6 ft 11 in (2.11 m) center, who played professional basketball for Mitsubishi Electric from 1996 to 2006 and was a member of the Japanese national team that competed during the 1998 FIBA World Championship.