Kamen Rider Build Side Story: A New Combination

The protagonist is actually Kiryu Sento's younger brother?! The younger brother of genius physicist Kiryu Sento undergoes an unusual transformation after being injected with Nebula Gas, thanks to his special constitution. Their original Best Match combinations can be split apart and recombined, with a chance of becoming a NEW Best Match. When he touches someone, he briefly witnesses their memories. Like Sento, he's also an invention fanatic. The main cast now has another troublesome junior! What kind of sparks will this younger brother, the protagonist, create with the others as he tries to rediscover himself alongside Sento? What fate awaits him…

This novel and its characters are entirely fictional. Any resemblance to actual people or events is purely coincidental. Do not imitate.