He is a fairly, lean muscular man with long black hair with a green shine. He has sky blue eyes with three circle swirls depicted on his face: two on his cheeks and one on his forehead. He first appeared with a eye mask on his face when he took it off to remind Kiriko Hattori of who he was. He wears the typical ninja raiment, which consists of a mahogany-brown top and dark pants with a matching color scarf around his waist. The portion in the middle of the short-sleeve shirt is a fishnet-like. He has mahogany-brown arm guards and black wrist bands, along with the ninja shoes and high socks or bandages protecting his lower legs. He also wields a katana, which he has it strapped behind his back.
Sutemaru is best described as a loyal by sticking to the Iga law codes of the village and a flirt when he easily becomes romantic with both Kiriko Hattori and Toshizo Hijikata. He is also very understanding as he listened to what Kiriko mentioned by wanted to be by Keiichiro's side and what Keiichiro told him about not wanting to stay in one spot, due to what Kiriko told Sutemaru to keep Keiichiro away from the baths. He also appears to have a big ego.
Not really much about his history except him and Kiriko were childhood friends and he kept her company after the loss of her brother. After time, Sutemaru developed a crush on Kiriko that he wanted children with her. To Kiriko, it was meant to be a joke. He is also the prince of Iga.
He originally appeared the beginning of Ep 7 by staring over the town of Nagasaki, then returned to notice both Kiriko and Keiichiro both speaking about how Kiriko kissed him to break the curse. He chuckles, then quickly bolted to kick Keiichiro into the nearby river. This caused him to carry Kiriko in his arms as he asks for a kiss from her when she flips him into the ground after he grips his teeth into the bottom of her kimono. Kiriko asks him for his name when he finally got up from the ground, having a sly smirk on his face. He then removes his mask as Kiriko quickly remembers her old friend by calling out his name while Keiichiro repeated after her in a confused way. Sutemaru asks for her to come with him, making her in a nervous position.
A little while later, the two headed in Otomi's room as Sutemaru broke the news to the retired Iga about the village being in chaos by Hitotsubashi Shigeyoshi and his men. Referring to the Shinsengumi, Sutemaru then tells Otomi that he couldn't protect them all and how he fought them off with his ninjitsu skills, making the people of the village to scatter. Sutemaru then tells both Otomi and Kiriko about the Shinsengumi and how dangerous they were that they killed a dojo owner named Gen'unsai Asai six months ago who sought out information on Shigeyoshi. Unbeknownst to him, Hyougo Asai listened on the conversation, making her drop the logs in her arms and pivoted away. Sutemaru explained to Otomi that the Shinsengumi's true objective is Nagasaki, and that they're coming to slay Keiichiro Tokugawa and to take Susanoo.
After speaking to Otomi when she inquired to him that he was in the town for something else, he exited Otomi's room and went to speak to Kiriko as she was looking out the window. He requested for her to abandon the Iga and leave with him, as he brought up they could be a happy couple somewhere. This caused her to be in a uncomfortable state and she told him that she isn't interested to be with no one. He then brought up the situation about her brother, causing her facial expression to change. Sutemaru then reminded her that it wasn't her fault and how his heart is warmer than the spring sun. Kiriko then pointed out that she cannot leave Keiichiro's side and he responded, saying that the village of Iga is gone and that how she doesn't need to do her job no longer. As Sutemaru starts to lecture her about Keiichiro, she patiently listens to him when she asks him for a favor.
Sutemaru appears on a rooftop with Keiichiro, telling him that he didn't introduce himself yet; explaining to him that he'll be the ultimate ninja someday and how he'll be Shogun. Telling him that he'll be a friend to him, Keiichiro counters calmly, saying that he already has a ninja when Sutemaru tells him that Kiriko is leaving with him. Realizing that Keiichiro is easily angered by this, Sutemaru then realize that Keiichiro wants to fight him when Sutemaru agrees, but not a fight; more of a talk.
As him and Keiichiro then appears in a forest, Keiichiro then tells Sutemaru that he wants to fight him, causing Sutemaru to warn him and say that he doesn't want to get in a brawl with him. As he begins to lecture Keiichiro about how much he knows about Kiriko, Sutemaru then explains to him about the ancient laws of the ninjas are a thorn within her heart. Sutemaru then went on to tell Keiichiro about Kiriko and her brother and how they were brought to the Iga Village. The laws were too strict that they did not allow a sister and a brother to care for one another to remain in the village (this resulted in the tragedy of Kiriko's brother stabbing himself in front of her). After he explained to Keiichiro, the two saw a flying battle ship in the sky when Sutemaru punches Keiichiro in the abdomen. As he tied him up, Keiichiro yells, telling Sutemaru to release him and Sutemaru countered, telling him that it was Kiriko who told him to keep Keiichiro away from the baths. This enraged Keiichiro, causing him to burst the ropes, which was wrapped around him and told Sutemaru that he didn't care what Kiriko mentioned and how he dislikes to sit back and let someone else get hurt before his eyes. This created Sutemaru's facial expression into being shocked.
Sutemaru finally appears on the battle field where both Keiichiro and Asai are facing Isamu Kondou and Souji Okita in their Onigami as he has a hold of Toshizo Hijikata. When she tells him to stop since he has a hold of her wrists, he kissed her causing her to be unconscious at the moment and he quickly unties Kiriko, due to Toshizo wrapping her up with a rope. Sutemaru then tells Kiriko that he slipped a drug in Toshizo and that it's fair since she slaughtered many in the Iga Village. As Sutemaru watches on with Kiriko, he then chanted to Keiichiro, saying to him to give the Shinsengumi heaven's punishment.
Kiriko Hattori- His childhood friend that he even developed a huge crush on. He wanted to be with her in fact, although she declined. Furthermore, he respected her wishes.
Kiriko's Brother- He knew of Kiriko's brother as he explained to Keiichiro on what happened to him. It is unclear if they had met before.
Otomi- He respects the retired Iga ninja and informed her with such disturbing information, which has to do with her grandson, Keiichiro.
Keiichiro Tokugawa- He played a little bit around with Keiichiro, temporarily. He then started to respect Keiichiro after listening to him explain himself about he felt about Kiriko.
Hitotsubashi Shigeyoshi- He despises what Shigeyoshi had planned and even worst when Shigeyoshi send his men to attack his village; creating things in chaos.
Isamu Kondou and Toshizo Hijikata- Knowing them in the Shinsengumi, he knows more of Toshizo Hijikata than Isamu. He caught her in his grasp and slipped a drug in her by kissing her. He mentioned to Kiriko how she deserves it on after what she done to the village of Iga.
Souji Okita- Not knowing too much of Souji, but he knows that she's a member of the Shinsengumi and that she's an enemy.
Although he shown to do little physical moves such as punching Keiichiro in the abdomen and kicking him into the water, Sutemaru is a strong ninja. His title as The Prince of Iga, and wanting to become the ultimate ninja has given him the right so. He mentioned to Otomi that he does ninjitsu, although he doesn't shows it in the series and he could be sneaky, such as slipping Toshizo Hijikata a drug, just by kissing her.