He was from the twelfth crop of foals sired by Deep Impact, who was the Japanese Horse of the Year in 2005 and 2006, winning races including the Tokyo Yushun, Tenno Sho, Arima Kinen and Japan Cup.

[4] Killer Ability began his racing career in a contest for previously unraced juveniles over 1800 metres on firm ground at Tokyo Racecourse on 27 June 2021.

Mirai Iwata was in the saddle two months later when the colt started 0.5/1 favourite for a maiden race over 2000 metres at Kokura Racecourse and scored his first success as he took the lead early in the straight and drew right away to win by seven lengths from Personal High in a record time of 1:59.5.

[6] On 28 December at Nakayama Racecourse, Killer Ability was stepped up to Grade 1 class to contest Hopeful Stakes over 2000 metres and went off the 2.1/1 second choice in the betting behind Command Line (winner of the Saudi Arabia Royal Cup) in a fifteen-runner field.

He started poorly before settling in mid-division and faded in the closing stages to come home thirteenth of the eighteen runners, beaten just over six lengths by the winner Geoglyph.