Because they are from different entries in the series, Kazuichi and Leon have never interacted with each other in canon. They also don't have any interactions in Ultimate Talent Development Plan.
Despite the fact that the characters have never interacted with each other, Bubblegum Rock is actually a decently popular ship within the Danganronpa fandom, and is also one of its most popular cross-ships. Numerous content has been created for the ship by fans, and its following rivals other popular shipping choices for both characters with a more canonical basis, such as Hagakureon, Kuzusouda, Leonaegi and Soul Friends.
A contributor to the ship's popularity could be the similarities between both characters in terms of design and personality. Both Kazuichi and Leon appear to be laid-back and carefree, but can also be highly compulsive when provoked. They both are also shown to be heavily attracted to women, and are often trying to find ways to gain their attention. Aesthetically, both characters have a similar "punk-rock" style, which some find visually appealing to look at. Both are also known for being major dreamers, as Leon has expressed his desire to quit baseball and pursue a career in music, while Kazuichi wishes to build a rocket, which he considers to be at the very top of the vehicle food chain.
- Kazuichi's English voice actor, Kyle Hebert, and Leon's English voice actor, Grant George, provide the voices of Kaito Momota and Shuichi Saihara respectively in Danganronpa V3: Killing Harmony. The latter two characters are best friends.