There is an awkward love triangle for both the seme, uke, and unwanted third wheel. However, in AKKK the said "third wheel" is much more demanding and threatening, and actually likes the SEME, not the uke.
Both mangas involve love triangles in which the seme is crushing on the uke, along with a third-wheel that's crushing on the uke. However, in Interval the uke initially likes someone else, while in SH:YCnB he doesn't really like anyone.
In both mangas, the ukes are sought after by another male that is not the seme. The love triangle continues until the seme witnesses the encounter where the "third wheel" is trying to get with the uke. Enraged, he saves his uke.