Splatoon Koshien

Splatoon Koshien is an official tournament hosted annually across Japan, where teams of all ages across the country (and online) compete in Turf War battles. The word 甲子園 Kōshien refers to a popular, annual Japanese high school baseball tournament, referencing the competition's format.

The first Koshien tournament began in 2015, four months after the release of. In all iterations of the tournament, gear secondary abilities are disabled.

Yearly fan books have been released by Famitsu, providing photo-filled reports looking back on each tournament and a directory containing team information.

2016
The Splatoon Koshien 2016 (スプラトゥーン甲子園 2016) commenced with first-round tournaments beginning 2015-09-13 in the Kyushu, Hokkaido, Tokai, Kinki, Tōhoku, Chūgoku, Shikoku, and Kanto regions of Japan. The finals, held on 2016-01-30, were won by the team いかたまkids (Ikatama kids).

In this tournament, all participants wore the same gear:, , and. Participants played and stages were randomized from a pool of five choices: Urchin Underpass, Saltspray Rig, Blackbelly Skatepark, Walleye Warehouse, and Arowana Mall.

After the finals, Splatoon producer and creator Hisashi Nogami was moved to tears by the incredible success of the event and the series as a whole, saying it came as a complete surprise to him. He thanked fans and the community for supporting the game so passionately, saying "I know we announced that content updates would end in January, but I'm wondering if we might be able to do just a bit of something more. Just please give us a little more time." This "thank you gift" was revealed to be the two volumes of Sheldon's Picks, released in mid-2016.

2017
The 2nd annual Splatoon Koshien 2017 (第2回スプラトゥーン甲子園 2017) commenced with district tournaments beginning on 2016-09-24 in the Tōkai, Hokkaido, Tōhoku, Kinki, Shikoku, Chūgoku, Kyushu, Chiba, and Kantō regions across Japan. The finals, held on 2017-02-11, were won by the team ダイナめう (Dynameu), who went on to represent Japan at the 2017 Splatoon 2 World Inkling Invitational.

Participants played Splatoon and stages were randomized from a pool of eight choices: Urchin Underpass, Walleye Warehouse, Kelp Dome, Flounder Heights, Museum d'Alfonsino, Mahi-Mahi Resort, Piranha Pit, and Ancho-V Games.

2018
The 3rd annual Splatoon Koshien 2018 (第3回スプラトゥーン甲子園 2017) commenced with district tournaments beginning on 2017-09-04 in the Tōkai, Tōhoku, Hokkaido, Kinki, Chūgoku, Shikoku, Kyushu, Chiba, and Kantō regions across Japan, as well as online. The finals, held on 2018-02-11, were won by the team GG BoyZ.

Participants played and stages were randomized from a pool of eight choices: The Reef, Musselforge Fitness, Starfish Mainstage, Humpback Pump Track, Inkblot Art Academy, Sturgeon Shipyard, Moray Towers, and Port Mackerel.

Hisashi Nogami has stated that participants in the competitions were exceptionally diverse in regards to age and social background, including teams comprised of four moms, along with a grandmother–mother–daughter trio.

The is based on the uniforms won by the winning team, who had initially won the online tournament. Along with trophies, the winning team was given custom Pro Controllers.

2019
The 4th annual Splatoon Koshien 2019 (第4回スプラトゥーン甲子園 2019) commenced with district tournaments beginning on 2018-07-28 in the Tōkai, Shikoku, North Kantō, Tōhoku, Shin'etsu, Chūgoku, Hokkaido, Kyushu, Hokuriku, Okinawa, Kanto, and Kinki regions across Japan, as well as online. The finals, held on 2019-01-27, were won by the team GG BoyZ for the second year in a row.

Originally scheduled for September 2018, the Hokuriku and Hokkaido district tournaments were rescheduled to December due to Typhoon Trami and the Eastern Iburi earthquake.

Participants played Splatoon 2 and stages were randomized from a pool of eight choices: The Reef, MakoMart, Piranha Pit, Humpback Pump Track, Inkblot Art Academy, Wahoo World, Manta Maria, and Walleye Warehouse. Over 1,100 teams participated in total.

Famitsu released the 4th Splatoon Koshien Official Fan Book on 2019-03-04, which included codes for the Japan-exclusive and.

2020
The 5th annual Splatoon Koshien 2020 (第5回スプラトゥーン甲子園 2020) commenced with district tournaments beginning on 2019-10-13 in the Kinki, Kyushu, Hokkaido, Kantō, and Tōkai regions across Japan, along with two online tournaments in the winter and spring. Due to COVID-19, the Tōkai tournament (originally scheduled for March) was cancelled. In addition, the finals (originally scheduled for April) were moved online and pushed to August 15–16, 2020. The finals were won by the team Another.

Participants played Splatoon 2 and stages were randomized from a pool of eight choices: The Reef, Humpback Pump Track, Inkblot Art Academy, Sturgeon Shipyard, Snapper Canal, MakoMart, Ancho-V Games, and Skipper Pavilion.

2023
The Splatoon Koshien 2023 tournament was announced on 2022-10-08, with further details released beginning in February 2023. It will be held in five regions across Japan and participants may sign up in either the General Team Division or Elementary School Team Division. Due to the number of entries, a lottery system will be used to determine which teams will participate.

Participants will play and stages will be randomized from a pool of seven choices. Five of these (Scorch Gorge, Hagglefish Market, Eeltail Alley, Undertow Spillway, and Mincemeat Metalworks) will be common to all tournaments, with the remaining combinations of two stages unique to each specific regional location.

Following the preliminary rounds of each tournament, participants will be invited to play impromptu, pickup sessions of Salmon Run Next Wave.

A commemorative banner was distributed via QR code on 2023-03-01 in anticipation of the event's kickoff.

District tournaments

 * Kantō region, April 29–30 at Makuhari Messe
 * Unique stages: Inkblot Art Academy, Flounder Heights
 * Hokkaido, June 17–18 at Sapporo Ryūtsū Center
 * Tōkai region, July 22–23 at Portmesse Nagoya
 * Kinki region, August 26–27 at Intex Osaka Hall 2
 * Online, September
 * National finals, December 16–17 at the Ota City General Gymnasium