Yandere-kun is the genderbend of the protagonist, Yandere-chan. It is not known if he will be implemented in the game or not, YandereDev message explaining that he would need more money and more time to implement a Yandere-kun.
Message of YandereDev.
"Many people have requested the ability to play as a male protagonist instead of a female. This would take a lot of extra time and money, since a male protagonist could not be added to the game without male equivalents of all of Yandere-chan's animations and voiced lines. However, if it was to happen, what would "Yandere-kun" be like?
One possibility is that Yandere-kun - exactly like his female equivalent - is an emotionless boy who feels no reason to live... until he meets Senpai, and finally begins experiencing the same emotions and sensations that everyone else can experience. Yandere-kun would seek to eliminate anyone who threatens to take Senpai away from him, because Yandere-kun doesn't want to lose the one thing that makes him feel alive.
Another possibility is that Yandere-kun is a naturally sadistic person who requires an obsession to give his life meaning. He has marked a girl to be "his" - his property, his possession. He's hunting down anyone who flirts with Senpai because it's like a game to him...a game of death.
What kind of person will Yandere-kun be? Will there even be a Yandere-kun? Only time will tell."