Mother's gift

Author is Mochida. Source is no longer available.
Danbooru post: https://danbooru.donmai.us/posts/7163649
Author's Twitter: https://twitter.com/Mochida_0703

Character: Seija Kijin

My interpretation is that Seija's mother gifted her this shirt. Seija doesn't like it because it looks childish, but have to wear it to not make her mom sad.