Takeda is related to "The Small Giant" in some way.
Their hairstyles look very similar,at least from behind; and given how all of the character designs are so unique, it's probably relevant.
Kageyama has Asperger syndrome
Taken from the character's page, "He has difficulty expressing his emotions in a healthy manner, and understanding the emotions of others. Outside of volleyball he's a very literal thinker. Volleyball seems to be the only thing he's interested in." Difficulty in social situations and narrow interests are symptoms of Aspergers.
Both are tall (Nasujima an estimated 5'11"-6' and Oikawa 6'), handsome with similar features, and have antagonistic personalities. They also serve as the Butt Monkey
of their respective series.