Crown-of-thorns is also known as Kiss-me-quick plant in Japan.
... BWAHAHAHAHAHAHAHAHAHA! I hope Kanda decides out of idle curiosity to google the meaning of her gift after Kai more or less introduced her to the concept of flower language, because otherwise she'd probably be very confused when Ookuma's misunderstanding drives her to awkwardly attempt to "rectify" the situation.
The hint is in flower language.Kanda-kuuuuuun!?
Crown-of-thorns is also known as Kiss-me-quick plant in Japan.