Sirius falling in love with Snape's sister was a rather complicated plot. In HP Doujinshi, Sirius and Lily's emotional entanglements often appeared, and Snape's sister, Pupu, often appeared in the story. Pupu was a strong and independent girl. She had a special relationship with Snape. Although she did not like Harry Potter, she had deep feelings for Sirius. In some novels, the relationship between Sirius and Poop developed so quickly that it even exceeded the distance between them. In other novels, however, the relationship between Sirius and Poop was not explicitly expressed. The relationship between them may lead to some complicated emotional entanglements and ethical issues that readers need to think about and judge for themselves. Sirius falling in love with Snape's sister is a very interesting and complicated plot that requires the reader to judge and deal with according to the plot of the novel.