In some fanfictions, Harry's friends might take on more of a protective role. They see how broken Harry is after Sirius' death and they become more vigilant about his safety. They might also encourage him to open up more about his feelings. Harry, on the other hand, could initially resist their efforts but eventually come to appreciate their friendship more as he realizes they are just trying to help him through this tough time.
In many fanfictions, Harry becomes more withdrawn after Sirius' death. He might lose his trust in the adults around him more easily, feeling that they couldn't protect Sirius, so he tries to be more self - reliant. He also could become more brooding and angry, his emotions more volatile as he grapples with the sudden and tragic loss.
His friends might not understand at first. They could be confused as to why Harry is being grounded and might try to convince him to break the rules. This could create some friction between Harry and his friends if he refuses, as they think he's being overly cautious.
In some fanfictions, their relationships become even stronger. They have been through so much together during the war that they are like family. For example, Harry, Ron and Hermione might see each other more often and support each other in their new careers.
It deepens their connection. They become more in tune with each other's feelings. For instance, if Harry is sad, Sirius can sense it and vice versa. This makes their relationship more empathetic.
In some fanfictions, Harry becomes more determined to fight against Voldemort. He channels his grief into training harder and becoming a stronger wizard. He often has flashbacks of Sirius which fuel his anger towards the Death Eaters and Voldemort, seeing them as the root cause of his loss.
After Sirius dies, Harry is in a really tough place. He feels like a part of his family has been ripped away. He may start to question his own actions that led to Sirius being in the Department of Mysteries in the first place. Harry will also feel a sense of loneliness, even with his friends around. But over time, he'll remember the lessons Sirius taught him, about being brave and standing up for what's right. This will give him the strength to move forward, and he'll use his memories of Sirius as a source of motivation in his fight against Voldemort.
The relationship could also take a more complex turn. Other characters might get involved in their conflict. Some might side with Sirius, thinking Harry was in the wrong, while others might try to mediate. This outside influence could either help or hinder the mending of their relationship, depending on how it's handled in the fanfic.
With Ginny, their relationship could be tested. Ginny might feel that Harry is becoming more distant as he delves into his new role. Harry, as the Master of Death, would have a different perspective on life and love. He might be more cautious about getting too close to Ginny, fearing for her safety. His friendships in general would be strained as he has to keep some secrets about his powers.
The relationship could become strained. Sirius might start to view Harry differently, with a bit of wariness. He might not trust Harry as much as before in terms of making good decisions. But it could also lead to a more open relationship where they talk about things they previously avoided, like relationships and feelings.
Well, at first, Sirius would be in a state of shock and panic. But then he'd have to step up. Their relationship would shift from one of equals (in a sense, as Harry was growing up) to a caretaker - cared - for dynamic. Sirius would have to learn about Harry's likes and dislikes as a baby. He'd sing lullabies to him, comfort him when he cries. This new experience would make their bond stronger in a very different way. Harry might not remember all of it when he's turned back, but there would be a subconscious change in how he feels towards Sirius, a deeper sense of security and love that stems from those baby - days when Sirius was his whole world.