This illustration was included in one of the pages in TG Zakki. It says that the flowers are called 紫蘭. Otherwise known as the Bletilla striata.
According to a Chinese site, if you give this flower to someone, it means “I won’t ever forget you, please let us not forget each other”.
Permission to upload was given by the artist.
Do not repost or remove source!
Work by 虫麻呂 (twitter)
19: Wearing a funny hat
Thanks for requesting Kageyama!! I really wanted to draw him.