Futarikkiri no Oishii Ojikan

Yukiteru Aoi is a college lecturer for the marine biology department. He loves the lunches at Akashi Kitchen, so he gets his lunch delivered from Kazuma Akashi who works there. For the past six months, they've been having special "lectures" on marine biology during Yukiteru's breaks. But, one day, Kazuma doesn't seem his normal self. As Yukiteru worries that Kazuma has gotten sick of him, one of his female students shows up in his lab and forces herself on him...!!

(Source: Renta!)