The contrast is appealing. It goes against the traditional gender roles. In normal stories, guys are often seen as the dominant ones. So, when an anime girl is in the dominant role, it's fresh and interesting.
Another theme can be self - discovery. Through the process of drawing the girl, the guy might learn more about himself, his feelings, and his artistic style. It could be a journey of understanding his own identity as an artist and as a person in relation to the girl he is drawing.
One common theme is the breaking of gender norms. In these stories, the anime girl defies the traditional expectation that the guy should be in control. For example, in 'Fullmetal Alchemist', Winry Rockbell is a skilled mechanic. She doesn't let the male alchemists around her overshadow her skills and knowledge, and she often stands her ground when it comes to decisions related to her work, which is a form of domination in a sense.
Another anime is 'The Garden of Words'. Here, the male protagonist Takao Akizuki, who is an aspiring shoemaker, often sketches in the garden where he meets Yukari Yukino. His sketches are influenced by her presence and their interactions, and it has a very poignant and artistic feel.
For this fanfiction, first, describe the setting of the auction. It could be a grand, yet seedy affair with all kinds of strange characters. The slave girl, with her big, sad eyes and timid demeanor, catches the guy's attention. He outbids everyone else. Once he has her, he takes her to his home. At first, she is scared, but gradually, she starts to show her true personality. She might be feisty and strong - willed. This surprises the guy, and he begins to respect her. Eventually, they could team up against the corrupt system that allows the auction of slaves in the first place.
One possible plot is that the guy in the van is actually under the control of a more powerful villain. The anime girl, who might be a key figure in the anime's lore, is kidnapped to be used as a bargaining chip. However, during her captivity, she befriends a small creature or another captive in the van. Together, they come up with a plan to escape and expose the real villain behind the kidnapping.
She may start by trying to figure out who the kidnapper is and what his motives are. If she has any special abilities or skills, she would be thinking about how to use them to her advantage. For example, if she has telepathic powers, she could try to send a distress signal to her friends or family. Also, she might try to gain the kidnapper's trust in order to find a moment to escape.
His life would be quite different. Socially, he would be surrounded by a different energy compared to a co - ed school. He may have to learn to communicate in a more empathetic way as girls often have different communication patterns. Academically, he might be in a minority in terms of his perspective, which could either make him feel left out or give him a chance to stand out. He would also probably have to deal with a lot of gossip and rumors as being the only boy would make him a hot topic among the girls.
First, you need to come up with a good story concept. Focus on the school girl characters' personalities, dreams, and relationships. Then, you should learn some basic art skills to draw the anime - style school girl characters. There are also software like Ren'Py that can help you build the visual novel structure.