Harunobu Nikaidō

He is a 4-dan in Class C-2. From the fifth volume of the manga, he is a 5-dan in Class C-1. His height is 152 centimeters as of the first season of the anime. He has been playing children's shogi with Rei since they were young, and he calls himself Rei's "heart friend" and "lifelong rival", often interacting with Rei in a forceful manner.

He is a junior disciple of Shimada and belongs to Shimada's study group. He prefers the Rook strategy in shogi.

He is the son of a wealthy family. Due to a kidney disease he has had since childhood, he has a plump physique and is always worried about his health, so his butler Hanaoka accompanies him. Some people notice that his body is weak, but it is not revealed to others at Nikaidō's own request, and only a few people like Shimada, the chairman, and Rei know the details.

In the commentary of the manga, the supervisor Manabu Senzaki points out that it is difficult to say who the model for each character in this work is, but he points out the similarity between Nikaidō and the late Kiyoshi Murayama.