His wardrobe usually consists of hoodies, t-shirts, shorts and pants, although he prefers to wear only boxers or be naked when possible.
Kotobuki is described as troublesome by Iori Kitahara as he and Shinji Tokita are usually the ones who initiate the partying and drinking. He is very boisterous and rowdy, although he does take diving seriously. As a bartender, he is very popular, as he does his jobs well and is a good listener when it comes to the troubles of his customers.
- Shinji Tokita: Not much was known about their past, but it seem like they are good friends who get along very well.
Grand Blue employees:
- The name Ryuujirou means "dragon" (竜) (ryuu), "next" (次) (ji) and "son" (郎) (rou).
- Ryuujirou's surname Kotobuki means "longevity, congratulations, one's natural life" (寿).
- Kotobuki works as a professional bartender part-time.
- Kotobuki is just like Shinji Tokita both in appearance and in personality when they are partying, but Kotobuki can be surprisingly charismatic.