Haruki Yamauchi is characterized by his dishonest and self-serving nature, with a tendency to lie and exaggerate, as noted by the interviewer who assessed him during the entrance examination. He often seeks shortcuts to success rather than putting in genuine effort, making him one of Class 1-D’s most unreliable students.

Similar to his close friends Ken Sudō and Kanji Ike, Haruki has a perverted side, showing a strong attraction toward Kikyō Kushida, whom he views as out of his league. As a result, he shifts his focus to Airi Sakura and Haruka Hasebe, drawn to their reserved and submissive demeanor. During the island survival test, he confided in Kiyotaka Ayanokōji, stating that he was pursuing Airi because he believed that being nice to her would eventually make her fall for him. Despite his usual immaturity, he has shown rare moments of self-awareness, such as when he accepted his rejection in Volume 4.5.

As the series progresses, Haruki’s selfishness and opportunistic behavior become more pronounced. After aligning himself with Arisu Sakayanagi and becoming her spy, he developed an arrogant and condescending attitude, referring to himself as Class D’s “lethal weapon” while looking down on his classmates. When defamatory rumors spread about his class, Haruki took pleasure in tormenting those affected, even shocking his closest friends, Ken and Kanji, with his cruelty.

In Volume 10, Haruki’s manipulative and gullible nature leads to his downfall. Deceived by Arisu, he was lured into betraying Class D under the false promise of a relationship with her. Convinced that Class A’s protection ensured his safety, he actively worked to have Kiyotaka expelled during The Class Poll. However, after being exposed and ultimately expelled from the school, Haruki reacted with rage and humiliation, lashing out at his classmates both verbally and physically before being restrained. His downfall serves as a testament to his short-sightedness, lack of self-awareness, and overall incompetence, making him one of the least respected figures in the series.

Haruki Yamauchi is a young man of average height with short brown hair and red eyes. His appearance is fairly unremarkable compared to his classmates, and he does not stand out in terms of physical presence.

He is most commonly seen wearing the standard Advanced Nurturing High School uniform, maintaining a casual and somewhat untidy look that reflects his laid-back personality.

In Volume 4.5, Haruki Yamauchi confessed his feelings to Airi Sakura, but she promptly rejected him. Despite initially pursuing her out of convenience, he quickly accepted her decision, later admitting to Kiyotaka Ayanokōji that he had only troubled her. Through this experience, he realized that expressing one’s feelings comes with responsibility, and he acknowledged that his feelings for Airi were shallow. He noted his lack of emotional reaction to being rejected, recognizing that he never truly liked her from the bottom of his heart. Following this, Haruki declared that he was “graduating” from meaningless crushes and would seek out a girl he could genuinely develop feelings for.

In Volume 10, Haruki played a pivotal role in the Class Poll special exam, where he rallied over half of Class 1-D to vote against Kiyotaka Ayanokōji, aiming for his expulsion. This was done under the manipulation of Arisu Sakayanagi, the leader of Class 1-A, who promised to secure praise votes for him in return. However, unbeknownst to Haruki, Sakayanagi deceived him, instead directing her class’s praise votes toward Kiyotaka as an act of revenge. Her grudge stemmed from their previous encounter in Volume 8, where Haruki had caused her to fall and made a crude remark about her.

As a result of his betrayal being exposed and receiving the highest number of criticism votes in Class D, Haruki was left unable to secure the 20 million points necessary to prevent his expulsion. He became the first student from Class D to be expelled from Advanced Nurturing High School.

Even in his final moments, Haruki refused to acknowledge his mistakes, instead claiming that he was being framed. He lashed out at his classmates, insulting them and insisting that Sakayanagi would save him, despite overwhelming evidence against him. After realizing her betrayal, Haruki became aggressive and attempted to attack his classmates, only to be restrained and removed from the school, marking the end of his time at Advanced Nurturing High School.

The name Haruki (春樹) is composed of the kanji 春 (haru), meaning “spring”, and 樹 (ki), meaning “tree”. This combination evokes imagery of growth, renewal, and vitality, which contrasts with Haruki’s impulsive and reckless nature in the series.

His surname, Yamauchi (山内), consists of the kanji 山 (yama), meaning “mountain” or “hill”, and 内 (uchi), meaning “inside” or “within”. This name can be interpreted as “within the mountain”, possibly symbolizing something hidden or overshadowed, much like Haruki’s tendency to rely on deception and manipulation rather than personal strength or intelligence.