A chibi version of Nagato Yuki in yukata clothing.

If I recall this is from the second season anime where they re-enacted summer vacation 15,000 times and caused Nagato to break down in the disappearances of Suzumiya Haruhi.

The Disappearance of Haruhi Suzumiya, or The Vanishment of Haruhi Suzumiya, is a 2010 Japanese animated film based on the fourth light novel of the same name written by Nagaru Tanigawa.

The second season anime series received a lot of complaints for repeating the same episode 8 times , the same episode where Haruhi repeated their summer.