|Kanji||関真澄 Seki Masumi|
|Occupation|| recycling collector|
|Education||middle school graduate|
|Age at Introduction||11|
Masumi Seki is one of Punpun's childhood friends and is best friends with Shimizu. He has a rough personality and a phobia of fire. His family owns Seki Lunches, which used to do business with the now-abandoned miso factory.
Seki has short, cropped hair in elementary school, which he gradually grows out over the course of the manga until it is past his shoulders when he is 22. He sometimes wears it in a ponytail and is fond of baseball caps, even owning a shark fin cap in the third grade. Seki has very nonobtrusive facial features, with a small nose and eyes, thin eyebrows, and a soft chin. He usually has a cool, indifferent expression even when upset. There is a permanent scar above the tip of his nose that is covered by a bandaid for most of elementary school. He is a bit lanky and tends to keep his hands his pockets. Many of his outfits are made up of an unbuttoned shirt over a T-shirt and cargo shorts. He wears the same coat throughout his middle school and high school ages since he cannot afford another. After getting beaten up at the end of Volume 12, he appears to be missing a tooth. However, in the epilogue, he smiles with all his teeth indicating either an artistic discrepancy or a fake tooth.
Seki has low self-esteem growing up, which he compensates for by acting tough. This idea is shown most plainly in a kindergarten flashback, where Seki's self-portrait is much, much smaller than the other children's, mirroring his opinion of himself. It is also noted by his own father and Shimizu's mother that he is actually shy as a child. He never enrolls in high school, deciding book smarts would only help him become a con-artist. Despite not being academic, his thoughts tend to wander in a very philosophical direction, which often depresses him. Physical labor distracts him from these thoughts, which is why he winds up taking many jobs when he's older. When his construction job gives him too much time to waste conversing with his coworkers about hypothetical questions and bad memories, Seki decides to quit, which he covers up by saying the job is too dangerous. These coworkers also think he is too cynical and pretentious. Seki looks for many ways to numb his mind, even considering getting married and having kids for this very purpose.
He is a rough and tumble child who is shown to get in fist fights as early as kindergarten. He even once threatens to beat his alcoholic father with a bat. Although he has no qualms fighting the female bully who stole Shimizu's money, he has never hit his girlfriend, and is shocked when she lies to her father about this to get Seki in trouble. Although he does not see himself as someone who abides by conventional morals, he does have a sense of honor. This is seen when he is ultimately unable to kill a man for pay, and when he later accepts Wada's sketchy "button-pushing" job under the one condition that it does not cause harm. It is also seen in his hatred of liars and his attitudes towards money in general.
It is Seki's deep belief that nothing in life is free. After watching his parents struggle to make ends meet, he develops strong feelings about money. When his friends decide to go searching for the money promised in the Lil' Chubster video, Seki helps them, in order to prove that the video is a prank and get-rich schemes don't work. In middle school, after watching two bullies scam Shimizu out of money, he boldly confronts them and says that money is something to be earned through hard work. Although he works multiple jobs, he never spends the money he earns. One thing that attracted him to the recycling business is that he can keep any throwaways for free. His sense of transaction rolls over into his relationships as well, since he offers to protect Shimizu in exchange for his company, although Shimizu is glad to spend time with him regardless. Although he constantly tells Shimizu to trust in him, Seki does not return the favor, believing on some level that Shimizu sticks around out of need instead of want, causing Seki to repeatedly point out how much Shimizu needs him and fostering an unhealthy, codependent relationship. After Shimizu abruptly breaks away from this relationship, Seki comes to terms with some of these fears when he saves Shimizu from a burning building and says he will be there to protect Shimizu even if Shimizu does not depend on him.
Seki begins smoking cigarettes in elementary school. After he and his friends explore the old miso factory, his dropped cigarette causes an explosion while Shimizu is still inside. This instance traumatizes Seki, causing a deep phobia of fire. He is beaten up twice, once in middle school and once at age twenty, when his aggressors pull a lighter out and compare his reactions to that of a dog. He tells his girlfriend he's attracted to her because she doesn't smoke, and when he breaks up with her, he's more concerned with her new smoking habit than her cheating. Wada also agrees not to smoke in front of him. When Seki's family goes broke, Shimizu suggests he sell pre-made lunches, but Seki is too afraid to use his family's portable stove. He later replaces the gas stove in his and his girlfriend's homes with electric stoves. He faces his fear of fire when Shimizu again is caught in an exploding building with the Pegasus Ensemble and Seki breaks inside to rescue him. In the epilogue, he is even shown smoking a cigarette.
|“|| Vain, prejudiced, and ignorant. They're a shining example of the arcehtypical dregs of society.|
-Seki, about his parents (Chapter 94)
Seki used to enjoy going with his father to the miso factory to get supplies. He would usually sit in the truck though instead of talking to the adults, and the other workers teased that Seki must be shy like his dad. After the miso factory went under and it became harder to get supplies and keep the family business afloat, Mr. Seki became depressed and turned to drinking. Seki begs him to reopen the store to reel in a little bit of cash, even threatening to beat him with a baseball bat. In middle school, his frustrated homeroom teacher tells Seki to bring his dad in for a meeting, and while Seki agrees to bring him, he warns it won't be productive since his father's a drunkard. When Seki is 15, his dad leaves suddenly, and his mom struggles to make money. In Chapter 94, it's implied that his father returned at some point when Seki tells his coworkers that his parents watch TV and gamble all day. By the epilogue, he and his father have allegedly reopened the store together.
Seki's mother is too busy with work to ever pick him up from kindergarten, so the teacher asks Shimizu's mom to make sure he gets home safely. When Seki is 15, his dad leaves suddenly, and his mom struggles to make ends meet. Seki bitterly jokes that they might be homeless soon if she can't pay rent. During this time, he decides to get his first job with the goal of living on his own.