Kamen Rider is a franchise that dates back to 1971, inspired by the live action Japanese series of Spider-Man (where Spider-Man had a giant robot)
Besides the first three Riders, every year or so a new series airs, featuring a new Rider, new enemies, new challenges. The reason bugs, is because Spider-Man, but the first two Kamen Riders were based on grasshoppers, and the majority of Riders are bug themed, or animal themed (like Faiz is a shark). The series continuity is...a big mess, with individual continuities, shared universes, cross overs, resets, branching timelines, and such, but generally, every season saved two were majorly self contained.
But the basic idea is it's the story(s) of men who are caught up in some evil scheme or scenarios, and as a result are granted powers, and use said powers to fight evil, and usually end on bittersweet notes, since being a hero does not guarantee a happy ending.