Natsusou Tsukuba

Natsusou is an energetic younger brother who shares the Tsukuba siblings' enthusiasm for karuta and for Akihiro's accomplishments. He and his brothers can be excitable spectators, readily expressing their support during matches.

His characterization is primarily shown through the family group rather than extended individual storylines. The brothers' confidence in Akihiro reinforces how seriously they regard him as both an older sibling and a karuta player.

Natsusou plays competitive karuta through the Shiranami Society. His membership gives him structured practice under the same organization associated with players such as Hideo Harada, though the series does not establish an advanced individual rank or signature playing style for him.

His experience nevertheless distinguishes him from spectators who know karuta only casually. Natsusou understands the basic competitive environment and follows his older brother's matches with direct familiarity with the game.

Natsusou appears primarily through Akihiro's family life. He and the other Tsukuba brothers support their older brother's involvement with Mizusawa and provide a glimpse of the household from which Akihiro comes.

The younger brothers also become connected to the Shiranami Society, extending the circle of young players influenced by the same karuta community that trained Chihaya and Taichi.

Akihiro Tsukuba is Natsusou's eldest brother and the sibling whose competitive karuta career he follows most closely. Natsusou Tsukuba openly supports Akihiro Tsukuba during his development with Mizusawa.

Fuyumasa Tsukuba and Haruomi Tsukuba are Natsusou's brothers. Natsusou Tsukuba, Fuyumasa Tsukuba and Haruomi Tsukuba frequently appear as a family group supporting their eldest brother.

Hideo Harada heads the Shiranami Society to which Natsusou belongs, placing Natsusou Tsukuba within the same broader training community as many of the series' established competitors.