Hm, 3 years ago I think, I've read a story, with uke is bigger than seme, and I think it's something related with sport, when the seme is done with the practicing he go to the uke room and find him using a toy, that how the first time they had sex I think, somebody help ┗( T﹏T )┛
Maybe http://www.mangago.zone/read-manga/ore_no_ushiro_ni_tatsu_na/mh/c005/1/ (and ch. 6)
Don't be scared mayu! There's a hell in from of yahΣ(  ̄□ ̄||)