Kevin as Ryoma's rival

They both have connections through their parents:

Nanjiro Ryoma's father defeated George Smith Kevin's father. It was the Samurai vs Spartan. This is why Kevin wants to beat Ryoma.

Ryoma and Kevin both want to settle things right. Also Nanjiro and Rinko met through Kevin's father. That's how they formed their love story in episode 129.

They have the same age.

They are both prodigies:

Ryoma is definitely known as a prodigy it was shown since the first few episodes on how great he was while for Kevin he became a captain at the age of 12. He easily defeats multiple schools aggressively and easily. Tezuka also didn't want Ryoma to have a match with Kevin right away, other than Ryoma lacks fighting spirit, he knows Kevin is strong.

They are complimentary opposites:

Ryoma the boy from East Asia, Kevin is the boy from US West Coast.

It's like the typical blonde haired blue eyed character that is loud with a big fighting spirit with a dark haired silent boy only focused on his goals.

Popular examples of these are Naruto and Sasuke or Noctis and Prompto from Final Fantasy. They usually represent the sun and the moon.

They inspire and motivate each other:

Ryoma motivated by Kevin's words. There was a time when Ryoma was criticised for being too complacent. When Kevin came a long and keeps taunting him, expressing how he really wants to beat him taught Ryoma that he shouldn't lose his fighting spirit.

Kevin also told him that they should fulfill their fathers' dreams, this gave a realization for Ryoma and he agreed to this statement.

Kevin was inspired by watching Ryoma. He was amazed before studying his moves. During their battle he was so mesmerized "Ryoma Echizen you are amazing", "Dad, did you also fought an amazing person".

"I will be watching you from a far but don't get complacent I will be catching up to you".

They work really well together:

This was shown in episode 173 when they were playing doubles with the Momoshiro and Kaido lookalikes.

Cons: Kevin is just a filler character. Still a good character though. (episode 141-160).

I did not like that all Kevin did was copy Ryoma's moves. He did one technique which is Illusion but that's it.

Kevin wants to fight Ryoma because he is Nanjiro's son, but he has another son Ryoga which kinda cliff hanger there.