Ruki+his pokemon

I really had a hard time deciding if Ruki would be a Psychic type gym leader, or a Dark type gym leader. The more I think about it, the more I think he'd lean more towards the Dark type pokemon.

Though I do see him sporting an Espeon sometimes.

Ruki-Dark type Gym Leader

Umbreon

• It's clear that Ruki favors umbreon out of the rest of his pokemon.
• Usually the first pokemon he sends out.
• Like Uruha, he had Umbreon since it was just an Eevee.

Thievul

• Because of his appearance, he secretly calls him Reita.
• Usually the third pokemon he throws out depending.
• Like with Umbreon, had him through his pre-evolution.

Houndoom

• Possibly his favorite pokemon second to Umbreon.
• Used a mega-evolution stone on him.
• Secretly calls him 'Aoi'.

Morpeko

• He honestly saw one in the wild one day and just had to have it regardless.
• This one he nicknames Kai.

Obstagoon

• Obstagoon is the only one of his pokemon who appreciates rock music like he does.
• Sometimes tries to teach him to sing, though never works out.

Alolan Persian

• Honestly like with Morpeko, when he saw the Meowth he had to have it.
• Persian likes to curl up close to Ruki while he relaxes.

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As a trainer I feel like Ruki's biggest rival would be Reita, or Uruha. He doesn't take himself too seriously however, despite how serious he looks.