Not much is revealed about Nikoru Yamana’s personal history, but she is prominently known as the best friend of Runa Shirakawa. The two share a close and longstanding friendship, with Nikoru often acting as Runa’s protector and confidante.

Due to her deep concern for Runa’s well-being, Nikoru is especially wary of any boys who show romantic interest in her friend. Her skepticism leads her to be overly cautious and sometimes intimidating toward Runa’s potential partners. Despite this, Nikoru’s actions stem from loyalty and care, and she ultimately wants Runa to find someone who genuinely makes her happy.

Outside of her protective tendencies, Nikoru is shown to be sociable and kind when interacting with those she trusts, especially within her close circle of friends.

Nikoru Yamana has light-colored, dyed hair that is noticeably lighter than Runa Shirakawa’s. She accessorizes with a necklace that rests at the opening of her chest, and she has visible ear piercings. Her fingernails are painted pink, complementing her trendy and fashionable appearance, which aligns with the gal (gyaru) style. Despite her stylish look, her sharp eyes give off the impression of a Yankee, a term often used in Japan to describe someone with a delinquent-like or intimidating presence.

Nikoru Yamana is portrayed as a cynical and judgmental individual, especially in her interactions with men. She displays a strong sense of distrust toward any male who becomes romantically involved with her best friend, Runa Shirakawa. This often manifests in her giving an intense, intimidating glare commonly described as a “death stare” to those she disapproves of.

Despite her harsh attitude toward others, Nikoru shows a much softer and more caring side when she is around her friends. She is particularly protective of Runa and is driven by a desire to shield her from emotional harm. While her protectiveness can be overbearing at times, it ultimately stems from genuine concern and a wish to see her friend happy.

Ren Nishina
Nikoru first met Ren Nishina through his close friendship with Ryuuto Kashima. Initially, she regarded Ren as a good friend and often stayed by his side, offering him companionship and emotional support. Over time, the two grew close, frequently spending time together.

By Volume 5, Nikoru begins to realize she may have romantic feelings for Ren. This becomes apparent when Runa Shirakawa teases her about their closeness over the phone, prompting Nikoru to fall silent. During their school study tour, Ren compliments Nikoru by calling her beautiful, causing her to blush further hinting at her feelings for him.

Their bond continues to strengthen in Volume 6, Chapter 3, where it is implied through Ryuuto’s observations that their relationship has developed beyond mere friendship. In Volume 6, Chapter 5, Nikoru and Ren officially begin dating, roughly one month after Ren ends his previous relationship with Saki Sekiya.

However, in later volumes (Volumes 9–10), Ren comes to the realization that Nikoru may not be fully invested in their relationship. Feeling unfulfilled, he ultimately decides to move on.

Runa Shirakawa
Nikoru and Runa have been close friends since middle school. Nikoru is fiercely protective of Runa, especially when it comes to her romantic relationships. Her cautious and often judgmental attitude toward Runa’s suitors stems from witnessing her friend’s past heartbreaks, where Runa would often rush into relationships that ended in abandonment. Because of this, Nikoru tends to distrust any guy dating Runa, often confronting or intimidating them until they prove themselves worthy.

Ryuuto Kashima
Initially, Nikoru harbored strong resentment toward Ryuuto, viewing him as just another “lowly nerd” unworthy of dating Runa. Having lumped him in with the rest of Runa’s past boyfriends, she was quick to judge him. However, her opinion began to shift after she invited Ryuuto to spend time with her. Although Ryuuto feared she was planning to confront or intimidate him, Nikoru simply brought him to a burger shop to talk.

There, she candidly admitted that her naturally intense gaze often gives people the wrong impression and jokingly asked to finish her fries before starting a serious conversation, claiming cold fries taste awful. She revealed that she had been observing Ryuuto to better understand him, noting that he was unlike the typical jocks Runa had dated. Ryuuto expressed how much he genuinely cared for Runa, prompting Nikoru to inform him about Runa’s upcoming birthday. When he asked for advice on what Runa liked, Nikoru called him a “strange guy” but agreed to help. This moment marked the beginning of a respectful and growing friendship between the two.

The given name Nikoru (笑琉) is composed of the kanji emi or warau (笑), meaning “smile” or “laugh,” and ru (琉), which is often associated with “precious stone” or “lapis lazuli,” and can evoke a refined or exotic nuance in names. The combination may suggest a bright or cheerful personality, though in Nikoru’s case, it contrasts with her more cynical nature.

Her surname Yamana (山名) combines yama (山), meaning “mountain,” and na (名), meaning “name” or “reputation.”