School Shoes
From Inkipedia, the Splatoon wiki
Template:Infobox clothing The School Shoes are a Shoes item that can only be obtained through the Inkling Girl Amiibo. It's ability is Ink Saver (Sub) (Decreases amount of ink consumed by your sub weapon.)
Complete these 4 missions the Amiibo gives you to unlock it:
13 Shifting Splatforms ~ Midnight Rendezvous ~
14 Octoling Assault ~ Skirmish at the Skatepark ~
15 Undeniable Flying Object ~ Bluefin Sighting ~
Boss 3 Roll with the Punches... The Rampaging Octowhirl!