Mantle is a hotel worker at
Weston hotel located in the Kalos region. He was unemployed and running wild 10 years in the past from the day
Ash Ketchum and friends visited the hotel. He was the owner of the hotel as he won a Pokémon battle in the past against
Weston. He made a deal with
Weston that if he lost the battle he'd stop bugging him and his customers but in return,
Weston would give up his hotels ownership, which he ended up doing.
Weston then became the hotel receptionist under
Mantle.
Ash Ketchum and his friends travel back in time 10 years with the help of
Weston's Rotom. They changed the past and created a new alternate future where
Weston was able to defeat
Mantle in the battle and keep the ownership of the hotel. He then hired
Mantle to work at his hotel.