As a child, he wore big round glasses, a suit and bow tie and had short seaweed green hair.
As a teenager, he no longer wears glasses, and so his eyes are shown to be yellow. He has short straight seaweed green hair, a cross mark under his left eye, and is mostly seen with his white Elite Shinigami High School uniform.
Matsugo has a calm and collected personality but is very passionate about the things he wants. Sakura and Tsubasa often compare him in this sense to a girl. He went to great lengths to change himself and get revenge on Rinne, but his attitude changed and he works hard to try and rekindle the friendship he and Rinne had when they were young. However, he tends to act like Ageha in regard to how he tries to revive his "friendship", much to Rinne's chagrin.
In elementary school, he was called Minimegane Chibio and was Rinne's classmate from first to sixth grade. As a young boy, Matsugo was small and had poor health and was bullied, but Rinne would stand up for him and endure his clinginess. One day 4 years ago, while on a training exercise to exterminate demons, Matsugo and Rinne teamed up to find and pop a devil balloon. The balloon ended up popping and knocking both of them out. When Matsugo awoke, Rinne pushed him into the nearby river where he had to be rescued by a teacher. Rinne seemingly threatened him to forget all about the incident. Believing he was betrayed, he decided to “be reborn”. He studied madly and got into the elite middle school affiliated with an high school, quit wearing glasses and switched to contacts and made himself taller and improved his look. Unbeknownst to him, one of his classmates Anju developed a crush on him, although she is too shy to even speak to him.
For the sole purpose of humiliating Rinne, he held a Shinigami elementary reunion at Hotel the Beyond. He seized Masato's wings, while he was setting a trap for Rinne, and left ¥3,000 and a ticket for Rinne to bring him to the reunion. Rinne came along with Sakura, Tsubasa, Rokumon and Masato, who immediately got kicked out for being a demon, and Matsugo impresses everyone by revealing how he changed. Upon learning Rinne used a Wasuredama to forget what happened 4 years ago, he orders his black cat named Kuromitsu to bring an Omoidasudama to make him remember. In actual fact, Rinne had awoken first to discover Matsugo had wet his pants in shock, and to save him from further bullying as the class arrived, he pushed Matsugo into the river to hide the fact. And he took a wasuredama to ensure he'd not tell anyone. Shocked by that news, Matsugo decides to stop dwelling in the past and shouts out that he likes Rinne, leaving everyone shocked.
When a High School Shinigami mixer is held with a fun networking event, Matsugo invites Rinne, who grows tired of his constant attention. So Rokumon gets the idea to ask Sakura to come with them as Rinne's girlfriend, in hopes of convincing Matsugo to stop being such a pest, to which she agrees. But with the assistance of Kuromitsu, he would keep them apart many times to be alone with Rinne, although Anju would tag along as well, trying to interfere. His plans backfired, but he eventually learned that Rinne and Sakura are not really dating.
He would continue being a pest to Rinne, as he seizes any opportunity to “deepen their friendship”, which is more meaningful to him than doing whatever duty he gets.
Once, considering Sakura to be a nuisance for his main objective, he conspired to make Sakura and Rinne's relation fall apart, by having them both invited to a Cultural Festival at the Elite Shinigami School, and taking them to a Traditional Haunted House called “The Promise of Hades”, where a boy must walk in front of his female companion and not turn around in order to win, but his plan backfired.
Eventually, he gets a new friend, who's none other than Anju having finally worked up the courage to shout into his ear with a megaphone that she wanted to be friends with him, and although they did a lot of things together, it didn't turn their friendship into a romantic relationship, and he simply considers her a dear friend like Rinne.
He was disappointed to learn that Rinne and Sakura hugged and complained about having preferred to deepen his friendship with her than with him.
- Shinigami Scythe: A tool used by all Shinigami, and most likely Damashigami too. Only twice he is seen wielding it.
- Pawn Vase (質壺): A bottle which sucks articles inside. It can however eject those pawned articles when the pawn ticket and the money are placed back inside.
- Spirit Bubble Solution (霊溶液シャボン玉): Anyone encased in a bubble gets sent into the reido once it's bursts.
- Shinigami Senses
Originally, Matsugo harbored a strong feeling of resentment towards Rinne, thinking he had nearly drowned him in a lake. When told by Rinne that he was instead helping him, Matsugo instantly changed his attitude towards him and declared that he loves him. He denies that it is true love and that he is "that way", but Sakura and Tsubasa aren't convinced. He goes to extreme lengths to spend time with Rinne, who gets annoyed and tries to avoid him.
He gets disappointed whenever Sakura is with Rinne, considering her a nuisance for his attempt to deepen his friendship.
He meets her right after reuniting with Rinne, and the two don't get along due to their similar crush on Rinne.
Anju has a crush on him. At first, Matsugo and Anju hadn't spoken to each other much, and so he seemed indifferent to her. Eventually much later, he became friends with her although he hasn't developed romantic feelings for her only considers her a dear friend like Rinne.
- "Quite a misunderstanding, it's friendship." (どんだ誤解だな、友情だ) – Chapter 188, when Tsubasa asks him if it's love
- "No matter how much passion they show me... I'll show him friendship beyond love" (たとえどんなに熱々な所を見せつけられて。。。今日をキッカケに恋にも勝る友情を育んでみせる) – Chapter 191, after Rinne goes flying with Sakura
- "I’m sorry, Mamiya Sakura. It was through my invitation to the Shinigami school cultural exchange, THAT A RIFT GOT BETWEEN THE ONCE-PASSIONATE COUPLE ROKUDO AND MAMIYA SAKURA!" (ごめんね真宮桜。死神学校交流会なんかに誘ったばかりにいつのまにか熱々カップルの六道くんと真宮桜さんの間に亀裂が！) – Chapter 195
- "Stupid Girl" (バカ女) – to Ageha
- "Hm?! The one who always follows Rinne around, Mamiya Sakura?" (ん！？りんねくんにやたらついて回る真宮桜さんか？) – Chapter 276, upon seeing Sakura
- "Rinne, for you to take your friendship with Mamiya Sakura than with me." (りんねくん, 僕より真宮桜さんとの友情を取るなんてっ。) – Chapter 398, upon learning that Rinne and Sakura hugged
- The incident with the Demon Balloon was 4 years ago in the manga, but 5 years ago in the anime.
- The Elite Shinigami High School is the school Renge and Kain were aiming at.
- Not even once has he turned visible to living beings.