Hikari has dark blue hair, light blue eyes and square frame glasses.
He is usually seen wearing a cyan tie with a white shirt and navy dress pants.
Hikari is an otaku who finds love where he least expects it: a flashy and beautiful girl named Iroha Igarashi who he initially states represents everything he hates about 3D girls. Although Hikari is at first skeptical of everything to do with the relationship, Iroha addresses him with nothing but kindness and the two become a couple. Hikari must navigate the barricades of his own insecurities while dealing with his new love life and carefully discovering people who can truly be his friends. He's finally able to find a glimmer of happiness in a life he previously lived in isolation and rejection, but he has to make due with the time he has because there's a catch: Iroha, the girl who has changed his life, is moving in 6 months!
Mitsuru is Hikari's father.
Kie is Hikari's mother.
Kaoru is Hikari's younger brother, who is the classmate of the younger sister of Tsutsui's bully Mitsuya Takanashi. Tsutsui does not have a very close relationship with Kaoru.
There are times when Kaoru seems to "secretly" encourage Tsutsui when suggestive things happen in Hikari's room with Iroha Igarashi, although Kaoru does not have much faith in his brother. In a time of major duress, Kaoru thinks of the damage to his own reputation instead of rallying to his brother's aid for support, and explicitly mentions that he does not want to grow up like Hikari.
Iroha is Hikari's girlfriend. When they met, Hikari was a little angry because she was "all the things she hates about 3D girls." But after Hikari saved her from her ex-boyfriend, she began to develop feelings for Hikari and finally asked him to be her boyfriend. She likes to make fun of him and gave him the nickname Tsutsun. She is very protective of him, even hitting the boys who bother him for being an otaku and even when he was accused of being a lolicon, she still insisted on going to his house with him after school, even though he wanted her to avoid him because she could damage her reputation. After the six months came, they were forced to leave each other. Until 7 years later, they would find themselves meeting each other. But this time Iroha becomes a complete different person, being mature and steady, not like the girl she was once. Alas, they would marry each other and that's where the story about the love of Tsutsui Hikari and Igarashi Iroha will end.
Ito is Hikari's first and best friend, who also happens to be an otaku. Yuto and Hikari are quite close, Hikari going so far as to cancel plans with Iroha Igarashi to make sure he does not neglect Ito. Ito expresses no jealousy towards Hikari for having Iroha as a girlfriend, and embraces everything in Hikari's best interest. Ito is one of only two people (the other being Iroha) who stays on Hikari's side and believes in him when he's labeled a lolicon.
Arisa is a classmate of Hikari. Initially, when Arisa first meets Hikari when he helps her up after she's fallen, she acts like all other girls and addresses him with disgust. Hikari is not disheartened by this reaction, however, noting that he is used to this type of rejection. However, later on and seemingly moved by his initial kindness, Arisa approaches Hikari after seeing him moping after classes during times when he has love troubles with Iroha Igarashi and asks him (in a less-than friendly way) what his problem is. She chooses to lend him a listening ear on several occasions when he seems to be down, lends him some advice, and even offers to cut his bangs much to the jealousy of Iroha. Arisa displays a very mild tsundere personality, since she looks down on Hikari at times while others she expresses how lucky Iroha is to date a nice guy like Hikari after he tried to comfort her during her distressing situation with her ex. Hikari later goes so far as to call her "his only female friend" and she becomes a regular part of the group. It is not explicitly stated, but somewhat implied that he is also her friend, although she does not seem to express any romantic interest in him.
- The name Hikari means "light" (光).
- Hikari's surname Tsutsui means "cylinder" (筒) (tsutsu) and "well, mine shaft, pit" (井) (i).
- Hikari is a video game nerd and he is scared to admit.
- In Episode 1, it is revealed that Hikari was once a classmate with a girl named Mika.