Japan will be recieving the Splatoon Koshien 2019 Fanbook on 4th March. It will feature coverage from Famitsu of the Splatoon Koshien 2019 Tournaments. The Fanbook will also have a serial code for some exclusive gear for Splatoon 2 which you can take a peek at in the image below.
The exclusive gear includes a parka and a Koshien Bandana. Each item of gear has the following abilities:
Ouen Parka (Squid ver.) (Cheering Parka, Octoling Ver.)
Brand: SquidForce
Gear Ability: Main Power Up
Rarity: 3
Koshien Bandana
Brand: SquidForce
Gear Ability: Swim Speed Up
Rarity: 3
It’s not the first time that exclusive gear has been available via serial codes in Japanese Magazines. Coro Coro Magazine also had exclusive Spy Gear for readers to redeem back in July, 2018. The book is available to pre-order via Amazon Japan for 1,620 yen (around $15 USD).
Source: Famitsu
