Narumi Seiwa is a very normal high schooler, if a bit dense. He has a puppy-like persona, which occasionally is shown in a comical fashion with Seiwa sprouting dog-ears, a tail, and a begging look on his face. He often admits himself that he is very naive and a little dense, which is confirmed when he says stupid things and asks really dumb questions (Tamura even thinks of him as the "naive idiot" at one point). He's a nice boy, very expressive, friendly, and will boldly announce what he's upset about. He has a very straight-forward personality and demands the reason for Tamura's apparent avoidance of him.
When Seiwa meets Tamura again (after Tamura fainted the day before), Seiwa wanted to find Tamura because he was so amazed someone could faint just by seeing someone else. Seiwa has a growing curiosity about what kind of person Tamura is which ends up with him following Tamura around and asking Tamura's friends about him. Tamura is very cold and tries to avoid him without letting Seiwa know why, since he's too embarrassed to say why. Seiwa is very upset about being treated this way, and wants to know why he's been treated so coldly and harshly, unlike everyone else Tamura knows (when Seiwa talks to Tamura's friends, his friends describe him as friendly to everyone).
When Tamura finally tells Seiwa why he's avoiding him, it takes awhile for it to register in Seiwa's brain and for him to realize just what Tamura's dream implies. Seiwa immediately believes that Tamura has foreseeing dreams, and isn't bothered in the slightest with going out with Tamura. Tamura is baffled at how Seiwa accepts so easily that he will be gay, but Seiwa isn't upset because before Tamura told him the reason for his behavior, Seiwa was already starting to like and be attracted to Tamura.
Seiwa sees the dream as a lucky blessing that will put him together with Tamura who he has begun to really like. This stresses out Tamura even more that he isn't actual upset like he thinks he should be. Seiwa is just a little too enthusiastic about going out with Tamura, especially on the physical level. Tamura has to ward him off constantly, especially when he finds out that Seiwa is inexperienced and doesn't know how to sleep with a man, which brings more problems.
Eventually they get through everything and start go out, including a physical relationship. While Tamura's sleeping off their first night together, Seiwa ends up meeting Tamura's family and wakes up to them celebrating the occasion, much to Tamura's embarrassment.
At the beginning of the story, Seiwa lives with his mother (twice divorced), an older sister, Nagisa, and a younger sister, Mio. Tamura doesn't meet Seiwa's family until seven years in their relationship when both of them are 23 and already living together. Seiwa has been avoiding letting Tamura meet his family, not because he's afraid or even worried about revealing his sexuality to his family, but because he knows Tamura is a good catch and that his mother and sisters are huge flirts. Seiwa often doesn't feel like he deserves such a great guy like Tamura since he considers himself pretty stupid at times, and his family tends to agree with him. By this time in the story, Seiwa is employed in restaurant services and is a chef apprentice.