[3] During his recovery, he watched the 2011 inaugural Krush Championship Tournament which inspired him to pursue his dream and become a professional kickboxer.
[4] After his recovery Kaisei, started to actively participate in amateur competitions, by 2016 he had already amassed multiple Kansai regional titles and awards.
In March 2017, Kaisei won the All Japan Shin Karate K-2 Grand Prix[5] this national title victory allowed to participate in the K-1 Koshien tournament later that year.
Following a disappointing result, Kaisei went back to amateur competition and won the 2018 K-1 Koshien tournament for a second time, making him the first to win this accolade two years in a row.
[10] Kaisei was then matched with top 10 ranked Jordann Pikeur for a shot at the 67.5 kg title on November 24 at K-1 World GP 2019 Yokohamatsuri.
He faced Kazuki Yamagiwa in the final and had to give up at the end of round 1 when he broke his hand and wrist hitting the top of his opponent's head.