Hailing from Okinawa, Ryūnosuke Tsunashi, nicknamed Ryuu, comes from a divorced family. His biological father worked as a debt-burdened fisherman, while his mother remarried the influential "Hotel King." Growing up at his stepfather's hotel, he gained English fluency through interactions with foreign guests. He maintains regular contact with his three younger brothers—Soutaro, Kounosuke, and Kotaro—during days off, often calling to share updates. His Okinawan upbringing also makes him highly sensitive to cold winters.

As TRIGGER's leader, Ryūnosuke adopts a manufactured "Wild and Sexy" public persona starkly contrasting his true nature. This image attracts frequent female attention and marketing campaigns like valentine chocolates themed around "a sexy night" with him, causing him visible discomfort. Privately, he exhibits shyness, timidity around women, and social naivete, repeatedly clarifying his persona isn't genuine by calling himself "just a boy from the country."

Kindness defines him, with a strong caretaking instinct toward younger individuals. He naturally assumes an older brother role professionally and socially, frequently mediating conflicts—whether between TRIGGER members Gaku and Tenn or IDOLiSH7's Tamaki and Sogo during collaborations. He respects IDOLiSH7's Mitsuki Izumi for similar brotherly qualities.

His disciplined routine includes early jogs from his Okinawan coastal childhood, followed by cooking breakfasts featuring family-sent ingredients for Okinawan dishes like stir-fried bitter melon. Idol activities—magazine shoots, variety shows, dance lessons—fill his schedule, while days off blend chores with socializing: drinking with Gaku or hosting meals for TRIGGER. He binge-watches dramas due to trouble following weekly broadcasts and excels at preparing fish.

Within TRIGGER, he shares first-name camaraderie; Tenn has removed him from group chats multiple times. IDOLiSH7 members address him formally as "Tsunashi-san," except Tamaki Yotsuba, who uses affectionate "Ryuu-aniki." He protected Riku Nanase during stress, ensuring safety and providing asthma inhalers. After forgetting Yamato Nikaido's birthday, Nagi Rokuya inscribed all IDOLiSH7 birthdays on his palm.

Distinct traits include photographic clumsiness, ticklishness on his feet's tops and soles, and a denim wardrobe for a casual image. He enjoys Awamori liquor but becomes troublesome when drunk—drawing on his stomach and dancing hara odori. Professionally, he posed seriously holding an eggplant in a shoot amusing his bandmates. He identifies with the mood-lifting flavor "Shequasar," aspiring to similarly uplift others.

Facing challenges, he champions resilience and teamwork within TRIGGER, declaring: "Let's combine our strengths as TRIGGER, and jump over that wall!"