Welcome to the Chem Lab(1994)

Kagakushitsu e Oide

School can be tough for students and teachers alike... Tsubaki and Kyohei have been close since university. Now, as teachers at the same school, they come to school together every morning, and leave together in the evening. The students have even created a wild setting where the two are romantically involved! While gentle and timid, Tsubaki tries to clear up misunderstandings, playful and charming Kyohei only does things to fuel the fire. Tsubaki, although flustered, knows that it's all in good fun. After all, they're just close friends...

(Source: Futekiya)

Note: Includes the one-shot "Let's Kiss (キスしよう！)".