[henshinzero]

Here are potential themes!

• Music Genres? Since the video games of Ex-Aid mixed with doctors, how would music genres work as we'll need key items that have devices based off of songs or bands/artists. The concept would have something like "music is in our hearts" or something and we'd have a summer movie that's a musical. The main protagonist can be a DJ, alongside riders who're a dancer, a solo musician, a music idol & a composer, etc. And yet Hibiki has musical instruments. Some Hibiki riders could guest star, as well as those like Poppy with her music.
• Film Genres? Same with Ex-Aid's VG genres, where we have riders based off of movies from action, drama, comedy, sci-fi, fantasy, romance, horror, etc.
• Sea Creatures? Can you imagine a rider series like Aquaman, where we'd have a hero who's born a half-breed from a sailor/navy or firefighting father and his mother a lost underwater city queen? Another rider can be a pirate like Black Manta with a female rider being a mermaid - like a princess. The riders can have suits similar to diver suits, casting them off to merfolk-based suits. Battles taking place on land & sea. Key items? I'd imagine either naval lights or fishing lures.
• Space Travel Rider? As we got Den-O who travels through time by a bullet train, how about the main rider be an alien from another planet who travels from planet to planet, galaxy to galaxy, as well as having human & extraterrestrial allies in his corner against intergalactic enemies. Almost like Kyuranger & Power Rangers In Space/Lost Galaxy.
• Tarot Cards? While Blade's all Minor Arcana & Playing Cards, we oughta have a tarot card theme this time and the main protagonist would be a lawyer with secondary rider being a fortune teller & assistant. Tertiary rider, a prosecutor and quarter rider a defendant who's a fugitive framed for a crime he didn't commit. The dark rider/antagonist rider would be the judge who'd orchestrate everything.
• Cooking? Taking inspiration from Shokugeki no Soma/Food Wars, Toriko & Fighting Foodons, the riders will be chefs & bakers who face monsters based off of recipes & creatures/machines/plantlife, etc.