[1] He won both of his races as a two-year-old in 2021, taking the Grade II Tokyo Sports Hai Nisai Stakes on his second start.

Prior to retiring in November 2023, he won all of his races as a four-year-old, the Dubai Sheema Classic, the Takarazuka Kinen, Tenno Sho, and the Japan Cup.

Kitasan Black, who was owned by enka singer Saburo Kitajima, won seven GI races during his career.

According to the manger chief Yuki Kuwata, based on how his body grew as well as distance aptitude, the goal was set to be Kikuka Sho, the same race his sire won in 2015.

Equinox made his debut at a 1800 meter long maiden race on August 28 at Niigata Racecourse with Christophe Lemaire as his jockey.

[8][10] Equinox's next race was the Tokyo Sports Hai Nisai Stakes (GII) held on November 20, where he was the most favored.

[17] Equinox then headed to the Tokyo Yushun (Japanese Derby) on May 29, where he was the 2nd most favored behind Danon Beluga, who had come in 4th place at Satsuki Sho.

He started the race third from last, and at the final stretch covered the last 3 furlongs at 33.6 seconds to close the gaps, but was beaten by Do Deuce by a neck.

After making a good start, he was in the middle of the pack chasing Panthalassa, who was running at a high pace of 57.4 seconds/1000 meters.

[21] During the post-race interview Lemaire commented "Spring was unlucky for him, but I was able to show the true Equinox" and "this may be his first GI, but this won't be the last.

[38] A few days later, the CEO of Silk Racing, Masashi Yonemoto, also announced that the horse would ultimately head to the Japan Cup if his condition was good after Takarazuka.

[39] The official fan polling which was held in the lead-up to the Takarazuka Kinen had Equinox consistently leading, with the final tally at 216,379 votes.

As the pack entered the final stretch, Equinox quickly passed Jack d'Or and Gaia Force,[45] and without letting Justin Palace catch up, he crossed the finishing line with a new world record of 1:55.2, marking his fifth consecutive GI win and becoming the third horse ever to win the Autumn Tenno Sho two years in a row.

[48] With this win, Equinox's total earnings in JRA races reached 1,252,692,000 yen, surpassing Contrail to become the 10th highest earner.

During the race, Equinox placed himself third behind runners Panthalassa and Titleholder, before taking the lead as the pack entered the final stretch and beat Liberty Island by four lengths, clocking in at 2:21.8.

[51] After the victory at the Japan Cup, discussions were made as to whether the horse should be entered in to the Arima Kinen or be retired to stud, with the head of Silk Racing quoted as saying all options were on the table;[53] it was ultimately announced on November 30 that the horse will not be entered to Arima and will stand stud at the Shadai Stallion Station starting from 2024.

[54] Upon Equinox's retirement, Kitasan Black's owner, Saburo Kitajima, made a statement to Nikkan Sports, celebrating and thanking the horse's career.

[60] This broke the previous record held by Deep Impact and Contrail's 12,000,000JPY for the highest service fee of any first year sire.