As part of the Rainbow Rocket Gang - Pokémon Center Campaign, players of Pokémon GO in Japan from February 26th, 2018 until March 11th, 2018 will have the chance to battle Sakaki's Nidoking in a Raid Battle at the Pokémon Center locations.

Sakaki's Nidoking is very powerful unlike ordinary Nidoking. Players will all need to team up together to defeat Sakaki's Nidoking. For those that do defeat it, a Nidoking sticker will be given out. To participate in a raid battle, players need to be level 5 or more and every time a player participates in a raid battle, one "Raid Pass" or "Premium Raid Pass" is required. A Premium Raid Pass can be obtained by using PokéCoins at the shop in-game.

Raid Battle Times:

Monday - Friday (except holidays): (1) 16:00 (2) 17:30 (3) 19:00
Saturdays, Sundays, and Holidays: (1) 11:00 (2) 12:30 (3) 14:00 (4) 15:30 (5) 17:00

Source: http://www.pokemon.co.jp/info/2018/02/180223_p02.html