I haven't watched the entirety of Bleach yet and I'm probably asking to be spoiled by bringing this up, but there's this reoccurring gag of a "new student" being introduced in Ichigo's classroom. (used during both filler and non-filler). They've skirted the lines a little with having Hitsugaya and Motsumoto join as temporary students already (with them appearing younger and older than ordinary high school students), but the ultimate end to this would be to pass off a character who looks extremely old as a new student.

Say hello to our new student. Treat him well! :D