Nothing to do with killer but something I would like point out about why Rui and Kodaka were decided to make them as killer.

Leon Kuwata were redesigned too many times and supposedly he is your decoy protagonist or comic relief buddy. When Rui and Kodaka hit their limit, they sick and fed up to design him again until they planned to mark him as a killer. Same goes for Sayaka, were also Rui and Kodaka's least character design. Hence you always see these two especially in DISTRUST's beta cover art which Sayaka trying to kill Leon.

Teruteru Hanamura were supposed to be handsome guy. There is one staff who likes Teruteru and thinks he looks like superstar actor, then Rui was like "Screw this!" and redesigned him as little pervert chubby boy we always know. In first blue ray of Danganronpa 3, Rui or Kodaka marked Teruteru is only one who never get new outfit design (Except as RoD obviously).

When I look at Leon and Teruteru, I curious who's our first killer in NDRV3 but might have share common with these two previous first killer, at least there must be reason they marked them as killer. Momota Kaito seems fit this category, hence too many fans think he is combination of Hagakure and Leon's character design. Also space rocket jokes, just ask Jin, Mikan and Monaca.