Ganpi is a Steel-type Trainer and member of the Kalos Elite Four.

Pokémon Trainer Satoshi has a new plan: see the world! But first, he and his partner Pikachu are headed to the opening of the Sakuragi Institute, a research facility dedicated to uncovering the mysteries of Pokémon in every region. Satoshi meets Gou, another boy with boundless curiosity about Pokémon, and both are overjoyed when Professor Sakuragi asks them to become official research fellows. With Satoshi as determined as ever to become a Pokémon Master, and Gou aiming to catch one of every Pokémon (including the Mythical Mew), our heroes are in for adventure and excitement as they explore the wide world of Pokémon!
 
(Source: Pokémon TV)
 
Note: Episode 119, 121, 126 and 128 are recap episodes that did not air outside of Japan.

The story is set in Diamond Ore Country, of which Diancie is the princess.This is a country located deep underground, where the Pokémon Carbink live together in peace. The energy source of this country is a giant diamond called the Sacred Diamond, which can only be created by princess Diancie. However, the current princess doesn't yet possess the power to create such a diamond, and the current Sacred Diamond's power is soon going to run out, which would result in the end of the country. Diancie meets up with Ash and Pikachu, and set off together with them to search for the legendary Pokemon Xerneas, which possesses sacred power, but on the way, they find the cocoon where the Destruction Pokémon, Yveltal, who was said to have once destroyed life in Kalos, lies in wait.
 
(Source: serebii.net)

Mezase Pokémon Master celebrates the final chapter in Satoshi and Pikachu's story, with their first companions and many Pokémon they have met throughout their journeys making their return.