They've had it for a while, even before ww2. Every year they compete for a chance to play in the koshien bowl, which is the national championship. They have fight songs and everything, and it's decently popular among the university students and alum i suppose.
GO KEIO UNICORNS ＼(^o^)／

https://inv.nadeko.net/watch?v=TJWzH0vd7Y4
(Fight song, even if it's at a baseball game): https://inv.nadeko.net/watch?v=vUAtqycIT7U