|Occupation||High School Student|
|Drama CD||Yoshimasa Hosoya|
Igarashi is a tanned-skin teenage boy with dark green hair, light yellow-green eyes and thick eyebrows. His body is quite well established due to him being in top physical shape as he is on the school's soccer team.
Igarashi has a competitive personality when it comes to sports and specially when he's trying to win Kae Serinuma over. She has described him as kind and good-humored. But when he is alone with Nozomu Nanashima and Kae, Igarashi becomes a kind, effective and smiley person. Igarashi had shown to be jealous whenever there is a romantic scene with Kae and one of his rivals. He isn't fond of the idea when Kae is alone with someone else other than him. Due to Shima Nishina's statement of how he only love Kae for her looks which is why he started to develop feelings toward her, Igarashi disagreed with that statement. However, he began to question his feelings toward Kae more especially after Kae became large again after the Valentine's Day arc. His feelings for Kae were put to the test and wondered more about his attraction to her. However, after spending time with her on the roof, Igarashi realized that regardless of Kae's appearance, Kae is still the same kind-hearted beautiful person he fell in love with. This causes him to accept her large physique and fall in love with her once again. People think of him as a kind yet tricky guy, having two "sides".
Kae is Igarashi's love interest. He was nice with Kae before her weight loss but he started to become interested in her once she gets thin. In other hand, Igarashi is the first on truly falling in love with her. He can be see as the most serious of the five, as he's always the first to try and separate Kae from the rest of the group. Igarashi is very hesitant on having physical contact with Kae to the point of invading her personal space, something that was notorious during the school festival, when he grab her hand without consent. After witnessing how much stressful was the festival for Kae, he was the first one to genuinely apologize to her.
During the group visit to Shima Nishina's house for Valentine's Day, Igarashi's feelings were questioned by Shima herself, when she claims that he only liked Kae for her appearance. When Kae returns to being large, he falls in love with her again. Yuusuke realizes that she's still the same person, admitting how admirable and interesting Kae actually is. After his love epiphany, Yuusuke became more softer and gentler regarding his interactions with Kae, something that was noticed by the others characters. His jealousy and possessiveness became less notorious too, as he show having fun while seeing Nozomu Nanashima and Kae dancing together, or when he take the initiative on helping to restore the friendship between Shima and Kae. During Kae's birthday, he is the only one who bought her an actual non-otaku present, an expensive pendant. When Kotoha (Igarashi's first love) was about to confess to him, Igarashi never wavered his feeling towards Kae, too the point that Kotoha herself see how much he loves her and admits that Yuusuke has already found his ideal girl. While Kae was kidnapped by Takeru Mitsuboshi, Igarashi and Asuma Mutsumi were the ones in the front of the rescue, and even after Mutsumi's accident he still stayed by Kae's side, angry that he couldn't do anything to stop her sadness.
Igarashi saved her twice from being sexually harassed: the time at the school cultural festival and the second was at Nanashima's house (although he was under the influence of his fever). He also often thinks of Serinuma first when she is missing, such as when they were separated on the island. They also do a daily "exercise" where they shake hands so Serinuma can become used to intimate contact with him.
Nanashima and Igarashi have been best friends since middle school. The two met while competing for a position on the school soccer team. Igarashi and Nanshima saw each other as rivals but also great friends. Unknown to Igarashi, Nanashima developed an inferiority complex toward Igarashi due to his envy that Yuusuke is a better athlete than him. Despite this, the two remained close friends. Both of them are well known and popular in school for their athlete ability. Due to Igarashi's "good guy" image, Igarashi usually scolds Nanashima when he said something offended or rude. Ironically, due to Nanashima's "bad boy" image and Igarashi's "good guy" image, the majority of the school know of their close friendship and how they are always with each other. Unknown for them both, Kae saw them as a couple. Due to her definition for coupling and her BL-mind, Kae usually saw them as a BL couple. However, after Kae came back to school from a week of absence and lost significant weight, Igarashi and Nanashima develop feelings for her. They competed for her affections along with her other suitors. Despite their rivalry, Nanashima and Igarashi help Kae in any way they can.
- "Serinuma-san Uh.. If you like, why don't we watch a movie together?" (to Kae Serinuma)
- "I had no intentions to continue playing nice with everyone."
- The name Yūsuke/Yuusuke means "assistant" (yū/yuu) and "help" (suke).
- Yuusuke's surname Igarashi means "fifty storms".
- Igarashi's name is written with the character for "5" which is why Kae's ship name for both him and Nanashima is 5x7.
- Igarashi's appearance is similar to Sosuke from the popular anime "Free! Eternal Summer".
- Igarshi's star sign is Taurus.
- Igarashi was born in May.
- Out of the 4 boys, Igarashi is the only one who is not a virgin.