Nakai is noticeably taller than most of his classmates, easily distinguishing him from others. He has short brown hair, and black eyes that appear to always be closed. It is revealed that Nakai has poor vision because of this.
Nakai has a very calm, friendly and laid-back demeanor who enjoys hanging out with his male friends more than he does with Mano. He explains that it's hard for him to hang out with Mano, although he still greatly cares for her.
~ Main article: Mano ~
Mano is Nakai's girlfriend. Nakai cares for Mano, though he struggles to hang out alone with her, as he finds it to be very difficult to please her sometimes. Regardless, they both appear to be very happy in each other's presence. As seen in the OVA of the anime, Nakai and Mano ride down a waterslide together, which is rumored to make those who ride it fall in love. In the final episode of the second season of the anime, Nakai and Mano attend the summer festival together and are seen happily watching the fireworks. It is revealed in Chapter 129 of the spin-off manga (over 10 year time skip) that Mano and Nakai are living together, but it is unknown if they are married.
~ Main article: Nishikata ~
Nishikata is one of Nakai's closest friends. As seen in chapter 48 and in the anime, when Nishikata first transferred into middle school, Nakai was quick to approach and become friends with him, as he was impressed with Nishikata being late on his first day of school. Since then, the two have hung out together many times, such as going to the waterpark together. Nakai is also aware of the obvious connection between Nishikata and Takagi and often tries to encourage and root him on to make a move on her.
- The surname Nakai means "middle" (中) (naka) and "well, mine shaft, pit" (井) (i).
- Nakai can still see even though his eyes are seemingly closed.
- This also explains why his vision isn't very clear (having to move upfront during the seating arrangement because he couldn't see the board).
- Nakai's age in the spin-off is never revealed, but estimated to be around 26 - 27 year old.
- His age being around 26 - 27 year old is due to the fact that he went to the same school and class as Takagi/ Nishikata. In Chapter 31, Takagi mentioned "it has been over 10 years since those days in middle school" while reading through her middle school graduation album. Since the age students graduate from middle school in Japan is 14 - 15 year old, then add over 10 years to it. 14 to 15 plus more than 10 is around 26, at the least.
- In the spin-off Chapter 129, it was revealed that Nakai is living together with Mano.
|Main||Takagi • Nishikata|
|Supporting||Mano • Nakai • Sanae • Yukari • Mina • Takao • Kimura • Hamaguchi • Houjou • Tanabe-sensei|
|Minor||Sumire Takagawa • Tunnel Fisherman • Tunnel Fishergirl • Tunnel Misc • Principal • Mano's Friend • Class 4-2 Unnamed Girl|