Ryuuichi Kuzuhara

Known as "Mr. Perfect." A skilled bartender who has been honored with a medal and even became a director of the Hotel Diamond Star. He has also published a cocktail book.

He has expelled inexperienced apprentices and discarded cocktails he deemed imperfect, adhering strictly to the ingredients and skills used. This is because he always holds a deep respect for his customers. Therefore, while he acknowledges Ryuu Sasakura's unique cocktails, he does not deny Sasakura's skills.

Eventually, due to the worsening management of Diamond Star, he protected Shiraishi (mentioned later) from layoffs, arguing that "we, the management, should take responsibility," and chose to retire.

In the final episode, inside Eden Hall R&T, he shows his apprentice Shiraishi the way forward, including reconciling with his father, and acknowledges Sasakura's growth to some extent by giving him one last task, watching over the growth of his juniors as he steps back.

Owner and bartender of "Bar K."

In the anime, he sometimes serves as a behind-the-scenes figure, explaining alcohol with Minoru Higashiyama, and occasionally acting as a storyteller with Miwa Kurushima and Higashiyama. He only showcases his bartending skills in episodes 7 and 11.

He is the character with the most significant difference in personality between the original work and the anime.