Resized to 53% of original (view original)
Artist's commentary
It's Nonna-san who is feeling bitter that Commander Katyusha grew up right before the match of Ooarai Girls vs Selection University and she couldn't see the moe sleeves.
Refers to the fact that while wearing the Ooarai school uniform in the movie, the end of Katyusha's sleeves go well past the tips of her fingers.