Seina Nakajima (Nagano, JPN) run at the 2021 Japan Curling Championships came to an end in the semifinals with a 8-2 loss to Sayaka Yoshimura (Sapporo, JPN). of the 2021 Japan Curling Championships in Wakkanai, Japan;
 
Nakajima finished 4-2 in the 0-team qualifying round. . In their opening game, Nakajima defeated Shinobu Aota (Aomori, JPN) 9-0, then won 20-1 against Kaori Nobuki (Okayama, JPN) and 10-8 against Tori Koana (Yamanashi, JPN). Nakajima won 13-5 against Ami Enami (Karuizawa, JPN). Nakajima went on to lose 8-6 against Yoshimura. Nakajima lost 7-4 to Satsuki Fujisawa (Kitami, JPN) in their final qualifying round match.
 
Nakajima ranks th overall on the Year-to-Date rankings with points earned so far this season.