Tomono debuted on the ISU Junior Grand Prix (JGP) series in August 2015, placing 13th in Riga, Latvia.

He was brought in to compete at the 2016 World Junior Championships in Debrecen, Hungary, as a late alternate after Sota Yamamoto withdrew.

Competing in the 2016–17 JGP series, Tomono placed fourth in Yokohama, Japan, and won the bronze medal in Ljubljana, Slovenia.

His breakout performances and result helped Team Japan secure three berths for the 2019 World Figure Skating Championships.

With Yuzuru Hanyu unready to compete and silver medalist Daisuke Takahashi declining international assignments, Tomono was sent to the 2019 Four Continents Championships, where he finished twelfth.

With gold medalist Shoma Uno declining the invitation, Tomono was sent to the 2020 Four Continents Championships, where he finished seventh, setting new personal bests in all segments of the competition.

[6] With the COVID-19 pandemic affecting international travel, the Grand Prix was assigned primarily based on geographic location, and Tomono competed at the 2020 NHK Trophy in an all-Japanese men's field.

[7] In the free skate, he doubled a quad attempt and turned out of another, among other jump errors, remaining in second place overall to take the silver medal, albeit nearly 50 points behind gold medalist Kagiyama's score.

[9] Tomono's first Grand Prix assignment was initially the 2021 Cup of China, but following its cancellation, he was reassigned to the 2021 Gran Premio d'Italia in Turin.

[11] At his second assignment, the 2021 Rostelecom Cup, he placed first in the short program and fifth in the free to finish third overall, setting new personal bests in all segments of the competition.

[16] Following injury-related withdrawals by national champion Yuzuru Hanyu and first alternate Kao Miura, Tomono was named to the Japanese team for the 2022 World Championships.

[18] A clean skate in the short program earned Tomono a new personal best and a small bronze medal for third place, sweeping the segment alongside fellow Japanese skaters Shoma Uno and Yuma Kagiyama.

Speaking afterwards, Tomono expressed gratitude for "this wonderful opportunity to skate at the end of the season" while also noting that he had "regrets that I couldn't put on my best in this performance.

"[20] In his first event of the season, Tomono came fourth at the 2022 CS Nebelhorn Trophy, including a third-place finish in the free skate.

[24][25] Tomono was fourth in both segments at the 2022–23 Japan Championships, but placed third overall, winning the bronze medal and standing on the senior national podium for the first time in his career.

[37] During the off-season, Tomono was cast to portray a younger version of the main character Kakeru, played by Daisuke Takahashi, as well as several other roles in the cross-genre ice show Hyoen - The Miracle of the Cross,[38][39] a loose adaptation of Kenji Miyazawa's novel Night on the Galactic Railroad.

During the off-season, Tomono sustained a hip injury and he acknowledged going into his first competition of the season, the 2024 Grand Prix de France that he did not have the optimal training time to practice his jumps.

[40] In October 2024 Tomono joined forces with Olympic champion Shizuka Arakawa, Olympic bronze medalist Daisuke Takahashi, Kana Muramoto, Takahito Mura, Keiji Tanaka, Yuna Aoki, Kosho Oshima, Yuto Kishina and Rena Uezono to launch the members-only official fan community F-Ske on the platform FANICON.