Railmin's Kamiwaza ability is to give anyone a train ride. As a Bugmin, he can set up a railway rollercoaster.
In the series
Railmin made his first camero appearance as a Bugmin in the beginning of episode 1.
Railmin's major role debut as a Bugmin was in episode 4 when he took both Wanda and Shuu on a railway rollercoaster. That was until Zuzumin stopped him with his droplets. Yuto then captures and debugs Bug-Railmin. Later, as his Promin-self, Railmin gave Yuto and his friends a train ride across the meadowy hills.
Railmin became Mirai's Promin buddy in episode 44 as Yuto passes him to her. Mirai uses Railmin to help her chase down Bug-Turbomin and Bug-Jetmin.