On the roof of the school where the students play the clapping game to determine the boss, a prominent piece of Japanese graffiti sprayed on the wall reads "If you're happy and you know it, clap your hands".
In the scene where Kimura gives his blazer to the baseball club freshman before climbing over the fence to join the Yakuza, there is Japanese writing embroidered on the jacket lining. This is the same poem that Kimura reads out in voiceover during the subsequent shots of him getting in the car.
The film's title literally means Blue Spring, but these two character put together without the grammatical ending of the adjective "blue" make the word for "youth".