Despite how he is, Tendou is actually a massive bookworm.
He has read all of the Harry Potter books currently released, the Percy Jackson series, Fifty Shades of Grey and the other sequels, even, including other infamous novels. In fact, most of his house's space is taken up by a large mass of books which he keeps in shelves and dusts and opens everyday in order to prevent molds and stuff from building up.
He is also a very huge nerd for Greek literature, especially the Greek Mythology. He has read every story for many times over and over again ever since he was in junior highschool. Due to this, he has also taken a liking to the language and is studying Greek somewhere no one knows about because he tries to keep this obsession from his teammates or anyone else if possible.
The only other person who actually knows of this is Ushijima.
When he told Ushijima he would be quitting volleyball after highschool (remember episode 10 in season 3?), he meant that because he was interested in trying to pursue a career as a novelist. He would also want to travel to Greece after graduating or when he finally gets a job.
Seriously, this little kid has high hopes for his future. *sniff* Everyone, follow his example at once.