Kushima Municipal Ichiki Junior High School - 串間市立市木中学校

Kushima Municipal Ichiki Junior High School closed in 2017 after being integrated into Kushima Junior High School. The summer uniform is a two-flat sailor uniform with a Kanto collar that opens in front, and features embroidery with tie closures. The embroidery looks like an "N" as far as I can confirm from the materials, but it is different from the initials of the school name and the design of the school badge, so it is unknown what it represents.

https://twitter.com/kumanoikuma/status/1513503812656721920