Kamen Rider Zi-O (2018)

I recommend Den-o to Zio because both of them are Tokusatsu. but the other reason I Recommend Den-o is because they use Time Travel concept. Also the main characters are Developing from weak to strong.

Zero-One is the series following Zi-O so if you want to watch the Kamen Rider seasons in order then you should watch Zero-One after Zi-O.

Zi-O is series following Build so if you want to watch the Kamen Rider seasons in order than you should watch Zi-O after Build

both are heisei anniversary seasons celebrating their respective decades both use returning actors

Both are seasons of a Toei tokusatsu franchise: Zenkaiger for Super Sentai and Zi-O for Kamen Rider. They have a heavy focus on being the anniversary of the franchise. Both seasons have a focus on the franchise being part of the bigger world/multiverse. They also have a gimmick that has the power of those seasons stored in them and they also transform into forms that are based on previous seasons' heros.

Both are seasons of a Toei tokusatsu franchise: Gokiager for Super Sentai and Zi-O for Kamen Rider. They have a heavy focus on being the anniversary of the franchise. Both seasons have a focus on the franchise being part of the bigger world/multiverse. Both seasons have many cameos of actors of the previous season of their franchise and both seasons' serve as a way to have continuations of the story for of these seasons. They also have a gimmick that has the power of those seasons stored in them.