Santa ga Irutte Shinjiteru?

The protagonist believed in Santa Claus until just a few days ago. But when he finally learned that his parents were buying his Christmas presents all this time, he confessed to his childhood friend that he doubted the existence of Santa Claus. Then his childhood friend makes fun of him while laughing hysterically. On Christmas Eve, someone knocks on the window of the protagonist's room from outside. When he looks to see who it is, the protagonist is surprised to see a female Santa standing there, she tells him that she will give him any present he wants. The protagonist says, "I want to be the kind of man that my childhood friend won't make fun of". The female Santa says, "Then I'll make you into a real man", and pushes the protagonist down on the bed...