Sometimes, Sirius's own secrets can harm Harry. In some fanfictions, if Sirius hides important information about Harry's family or his own past, and Harry discovers it later in a bad way, it causes emotional pain. A good example is 'The Hidden Truths' where Harry finds out Sirius knew something crucial all along.
First, be very specific with your search terms. Use the exact phrase'sirius finds hurts harry' in the search bar of fanfiction platforms. Also, check if the platform has filters like genre, rating, etc. and use them to narrow down your search. For example, if you only want to read completed works, set the appropriate filter.
The 'sirius hurts regulus fanfiction' often delves into the family aspect by highlighting the expectations placed on them as Blacks. Sirius's actions, like running away from home, can be seen as a betrayal in Regulus's eyes. This causes a rift between them. The fanfictions explore how family loyalty and the need for acceptance within the family are intertwined with the pain that Sirius's choices inflict on Regulus.
One popular story might be 'The Unintended Consequence'. In it, Sirius's actions, perhaps out of overprotectiveness, end up causing emotional harm to Harry. For example, Sirius might try to keep Harry from certain adventures, which makes Harry feel restricted and misunderstood.
Snape might be secretly pleased at first, seeing as he has no love for Sirius. But then, being a teacher, he'd probably feel obliged to report it. He also might use this situation to his advantage against Sirius in the wizarding politics within Hogwarts.
Sirius could help Harry cope by sharing his own experiences of being an outcast in his family. He could tell Harry that just because his parents did this horrible thing, it doesn't mean he's unlovable. Sirius could also introduce Harry to his friends in the wizarding world, like Remus, who could also offer support and friendship.
It's possible that in the cave, they start to see each other as equals rather than just a mentor - student relationship. They might argue about the best way to deal with the cave's mysteries at first, but through that process, they learn to value each other's perspectives. Also, if one of them gets injured in the cave, the care and concern shown by the other would enhance their relationship.
You can try some popular fanfiction websites like Archive of Our Own (AO3). Just use the search function on the site and type in 'sirius finds hurts harry'. There's a good chance you'll find relevant fanfictions there as it has a vast collection of various fan works.
Harry may also feel a sense of adventure. Despite the situation, he's used to facing strange and dangerous things. He might start to think about how he can use this situation to his advantage, like finding out more about his parents or the secrets of the wizarding world that Sirius might know. He could be a bit excited as well as scared. For example, he might be thinking that this could be a chance to get away from the Dursleys for good.
It may explore the emotional bond between them. Sirius could be like a father figure to Harry. He gives Harry advice and guidance, which is different from what Harry gets from others. This special connection makes Harry trust Sirius more than anyone else.
Maybe Sirius gets help from some powerful wizards or witches who believe in his innocence. They might testify on his behalf in front of the wizarding authorities. Sirius also could show his strong emotional bond with Harry. He has always been there for Harry in spirit, and now he can be there physically to raise him, which convinces the authorities to give him custody.