Tiennan Costley

Early life Costley was born in 2000 and raised in New Zealand. He was educated at Auckland's Westlake Boys High School, playing rugby at the school alongside future England player Chandler Cunningham-South.

Career Early career In 2017, Costley had been named in the North Harbour U18s squad.

After graduating from Westlake Boys High School in Auckland, Costley originally hoped to progress through New Zealand rugby and eventually play for the All Blacks, captaining the team in his final year in their first ever appearance in the All-Japan University Rugby Championship, the highest level of youth competition in Japanese schools.

Kobe Steelers In January 2023, Costley, alongside , were announced as the latest signings for the Kobe Steelers. At the time, the Steelers had been in the early stages of their 2022–23 season. By March, and nearing the end of the season, Costley had made his senior debut for the Steelers, after an injury to regular back rower Marcell Coetzee. excelling at the breakdown and consistently breaking opposition defensive lines.

In 2024–25, Costley remained a regular starter, though his role became increasingly versatile. Similar to his responsibilities with the Japan national team, he featured across all three back-row positions. While he was deployed most frequently on the blindside (No. 6) and openside (No. 7), he also made a solitary appearance at number eight. He was also one of the league leaders in carry metres, defenders beaten, post-contact metres, line breaks, as well as turnovers won. Following the regular season, Costley won the "Best Tackler Award". At the post-season awards, Costley was named in the league's best XV alongside teammate Ardie Savea.

International career In January 2024, Costley was named in a Japan training camp by coach Eddie Jones. In May, following the 2023–24 JRLO season, he was named in another training camp ahead of Japan's Tests in the June–July international window. In June 2024, Costley was named in Japan's starting squad to play England at the National Stadium. Costley made his Test debut on 22 June 2024. Japan lost 17–52.

The following July, Costley played in one of the Japan XV's two matches against the Māori All Blacks, coming off the bench in the 50th minute. Costley played in all four of their matches,

Despite not being in Japan's squad for their two-Tests against Wales, Costley was later named in their 37-man squad for the second edition of the Pacific Nations Cup. Costley played less than twenty minutes a match in three Tests, and made a further two caps for Japan in the 2025 Autumn International window against Australia and South Africa respectively. In the latter match, Costley was reported to have been used as a "hybrid player", covering the wing position when he was substituted on.

Career statistics Club

+ Appearances and tries by club, season and competitionClubSeasonLeagueDivisionAppsTriesPoints Kobe Steelers 2022–23 Japan Rugby League One 5 0 0 2023–24 16 4 20 2024–25 18 3 15 2025–26 19 7 35 Total 58 14 70

International updated|18 July 2026.

Individual

Japan Rugby League One Best XV: 2025–26 Japan Rugby League One Best Tackler Award: 2025–26