The Masumi are a ninja clan loyal to the Kamunabi, known for a willingness to die for their master. After Kunishige’s death, three of them, Ro, Moku, and Sumi, guard Seiichi Samura at Senkutsuji Temple. When the Hishaku attack, they suppress sound and scent so a blind man can fight by hearing. They are prepared to die so he can leave. He refuses the sacrifice, rescues them, and later releases them from service. After his apparent betrayal, they join Chihiro for Operation: Easy Does It: protect Iori, the daughter whose memories of her father they themselves erased.
That last clause is the clan’s whole moral. They are good at their job. The job included making a child forget a Buddhist swordsman so she could live through a war-crime backlash. The job later includes putting her on a motorcycle away from Kuguri. They do both. It will call it the Masumi.
Ro
Leader. Over twenty-three. Looks like a child. Chihiro and Iori mistake him for one. He dislikes being treated as a kid and will still use the appearance to skip work. At Senkutsuji he takes on a Samura persona: sunglasses, candy cigarettes, “get fired up,” blunt manners. After the temple falls he visits Chihiro in hospital and says the Masumi will look out for him, per Hakuri’s request. He is the one who recovers Kumeyuri after Samura takes it off Hiruhiko at the hotel. A ninja clan’s leader doing inventory on a banquet sword is this book’s idea of logistics. He is not comic relief. He is what loyalty looks like when the master has sunglasses and a death wish. File: Ro.
Moku
Tall. Meets Hakuri and Uruha at the train station with Sumi. Rallies Senkutsuji’s troops when the Hishaku hit. Deeply empathetic in the way this book allows: when Chihiro starts doubting or chewing himself, Moku reminds him of the mission or shuts him up with food. The goldfish household’s manners, applied by a ninja. He is the clan’s gravity. Ro is the face. Sumi is the map. Moku is the reason Chihiro eats. File: Moku.
Sumi
Kunoichi. Cross-shaped tattoo on the right side of the face. Transportation mandalas, drawn with a marker: that is how Hakuri and Uruha reach Senkutsuji from the station. She tends Hakuri’s treatment so Storehouse can be used without killing him. In Operation: Easy Does It she takes Iori on a motorcycle while Kuguri gives chase. Blood tracking versus a drawn door. She is the reason the hotel is even a possible veil. Sengoku’s Reigen house is the building. Sumi’s marker is the road. File: Sumi.
Operation: Easy Does It
Samura’s Owl is up. The Hishaku want Iori as a lever. The Masumi take her out of school toward Kyoto. Chihiro goes with them to tell her the truth rather than re-seal it. Kuguri and Toto hunt. The Kyoto Bloodshed Hotel is the chosen dark. Iori’s seal frays because she still loved her father and breaks when she shields Ikura. Hiruhiko wrecks the upper floors. Samura arrives. The Masumi do not get a volume jacket. They get the girl out of the myth long enough for her to choose a sword. After Samura dies, Tobimune is hers. The clan that erased him is still in the courtyard. That is not irony for its own sake. It is the job, finished as protection instead of erasure.
They are Kamunabi-aligned and Samura-loyal and then Iori-loyal. The bureau page lists them as Sanso-adjacent staff. This page lists them as people. Official chapters: VIZ / MANGA Plus.