Sanemi is the math teacher at Kimetsu academy. He is dating the P.E teacher, Giyuu Tomioka. Sanemi has a younger brother, Genya Shinazugawa and 16 years old. Sanemi and Giyuu are now living together with Genya to take care of. Sanemi would scold Genya if he got a question wrong for his class..like he did with the other classes he has with Math while Giyuu actually helped Genya to study. Despite the scolding, Sanemi still loves Genya deeply. One thing Sanemi did not know was that Genya was dating another boy in his classes, Muichiro Tokito.

It was a normal day but Sanemi decided to make a math test for the students to test their knowledge on the topic they covered. The students were taking the test quietly then once class ended, Sanemi took the tests and graded them, he paid most attention to Genya's test to see if he had been improving. After grading everything, Genya got the highest out of his 3rd period math. He was impressed.

Later during lunch, Genya was hanging out with a friend, Muichiro and they were chatting as per usual. Sanemi went to go see his boyfriend, Giyuu. He told him about all the math classes he had before, talking about how chaotic it was, how they went on the tea, etc. Giyuu explained about what happened during his P.E periods as well before they just chatted about random things out of school. Genya was having fun with Muichiro behind the two teachers, holding hands and smiling. "...."