There's this story about Oda Nobunaga, Toyotomi Hideyoshi and Tokugawa Iasu. They were asked about the same question: what are you going to do if a cuculus won't sing? Hideyoshi said "I'll trick it into singing". Iasu said "I'll wait patiently". And Nobunaga said "I fucking kill it". Hence the word on the shirt, cuculus killer.