Bet

His first day in Japan Grimmjow made a stupid bet with Renji, which caused Grimmjow and Ichigo to have an awkward first encounter. Of course Ichigo just so happens to be going to the same music school Grimmjow's attending and just so happens to play the same instrument as Grimmjow as well. Grimmjow can't stand Ichigo and his condescending attitude and iron will to steal first chair from him. However, that nearly permant scowl has Grimmjow intrigued, and practically failing intro to chem gives him a reason to see Ichigo more often as well as becoming each others sparring partners. Going to a music university in Japan was certainly one of Grimmjow's best decisions.
(GrimmIchi)
(I don't own bleach)
(I only put M because I use a lot of foul language)
(Please comment, I'd like to know you're thoughts!)