Squid Girl

Squid Girl, also known as ''Shinryaku! Ika Musume (侵略!イカ娘 Invade! Squid Girl'') is a Japanese comic series by artist Masahiro Anbe about a young squid girl that emerges from the ocean in order to invade Earth to punish them for polluting the ocean, but ends up working at a shop nearby in order to work off a debt. The series has also been adapted to animation.

Squid Girl outfit announcement
On April 1st, Masahiro posted a drawing of an Inkling wearing a School Uniform to his Twitter account. This was followed in May with Squid Girl and Splatoon crossover artworks by Masahiro, including artworks in the comic magazine, Weekly Shounen Champion.

A page in the Weekly Shounen Champion magazine announced an upcoming Splatoon release:

"そしてついに「侵略！イカ娘」コラボコスチューム制作開始！　無料アップデートでオリジナルコスチュームの配信が決定！　果たしてどんなビジュアルに！？配信開始予定の８月を待て！"

- Weekly Shounen Champion

In English, this translates as:

"And finally, the "Squid Girl" collaboration costume production has begun!

It has been determined this original costume will be delivered as a free update! What is it expected to look like? Wait for the planned distribution to start in August!"

- Weekly Shounen Champion (Translation)

SQUID GIRL Gear
On August 5, 2015, three pieces of gear based on Squid Girl were released, including the SQUID GIRL Hat, SQUID GIRL Tunic, and SQUID GIRL Shoes.