It could be that Severus buys Harry something as a gesture of reconciliation. Another possibility is that the item is crucial for a magical task or adventure they need to undertake together. Sometimes, it's just a way for the author to develop their relationship in a unique way.
Maybe it's because Severus wants to show his hidden care for Harry. Or it could be part of a larger plot to protect him from some unknown danger.
Maybe in that fanfic, Harry faces extreme hopelessness and feels there's no way out of his difficult circumstances, leading to the attempt.
Well, this twist could lead to interesting plot developments. Maybe Severus has to balance his loyalty to Harry with his past ties to Voldemort. It could also change the way Harry perceives the magical world and his place in it.
Maybe he wants to understand the character of Bellatrix better from the perspective of fans. Fanfiction often explores different aspects of a character that might not be fully shown in the original work.
Severus' character undergoes a major transformation. He begins to value relationships more, especially his newfound father - son relationship with Harry. He may start to interact more with the other students in a less intimidating way because he realizes that being harsh all the time isn't good for anyone, especially Harry. He also becomes more involved in the non - potions aspects of Harry's life at Hogwarts, like helping him with his other studies or dealing with bullying from other students. This shows a side of Severus that was previously hidden, a side that cares deeply for someone other than himself.
I'm not sure if Harry actually buys Tonks fanfic in the official 'Harry Potter' canon. Fanfic is a product of the fandom and not part of the original story. It could be a fun 'what - if' scenario that a fan has come up with, but there's no evidence in the books or movies to suggest that Harry would be buying Tonks fanfic.
It's hard to say for sure without reading the specific fanfiction. It could be that the three taps are a symbol of something significant between them, like a hidden message or a way to communicate in a unique way in the magical world the author has created.
In many Severus and Harry fanfics, their relationship is often re - imagined. Sometimes it's a mentor - mentee relationship that goes deeper than in the original books. For example, some fics might explore how Severus, with his complex past and knowledge, can help Harry grow not just as a wizard but also as a person, despite their initial animosity.
The fanfic might reimagine Harry as a character who is constantly at odds with himself. He has the potential for great power from Tom, but also the emotional depth and loyalty from Severus. This internal struggle could be a major part of his character arc, as he tries to figure out who he really is and how to use his abilities for good, despite the dark shadows of his parentage.
Perhaps he wants to start a new school or a training center for young wizards and witches, and a mansion would be a perfect place for that. It could provide ample room for classrooms, dormitories, and training grounds.
Severus might start off as just fulfilling a sense of duty. He has always been a complex character. But as he saves Harry from the Dursleys, he begins to see Harry in a new light. He realizes that Harry is not just James Potter's son but an individual with his own struggles. This could lead to him becoming more empathetic towards Harry, gradually shedding some of his cold exterior.