Muneakira's childhood friend and the eldest daughter of the Tokugawa Shogunate. She seems to have feelings for Muneakira, and acts very much like a tsundere towards him. She is a self-proclaimed spoiled princess and always seeks to get her way regarding any decision she wants to make. She gets extremely jealous of any girl who tries to get close to Muneakira, and generally acts upon this jealousy by flying into a rage. Later, she reveals her true feelings to Muneakira and kisses him, thus becoming his third Master Samurai. Her weapon is a naginata decorated near the blade, and her transformation phrase is "Tenga Ryūrei", which means "Elegant Beauty". In the second season she is able to transform into a Master Samurai at will with no phrase required. Sen's attacks usually revolve around thunder or lightning.