Finding such a specific fanfiction can be a bit of a challenge. You could also try joining some Harry Potter or God of War (since Atreus is from there) fan forums. There, you can ask other fans if they've come across any fanfiction with this plot. Maybe someone has written it privately and can share it with you.
I'm sorry, I haven't read a specific 'harry potter saves atreus fanfiction' myself, but you can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own. There might be some interesting stories there.
In such a fanfiction, it could be that Atreus has somehow ended up in Hogwarts. There could be a conflict between the students who are suspicious of this new arrival and Harry has to step in to protect Atreus. Harry would likely use his knowledge of the magical world and his courage to ensure Atreus's safety. He might also introduce Atreus to the wonders of magic, like flying on a broomstick or using potions to heal wounds.
In this fanfiction scenario, Harry Potter might use his magic to heal Atreus if he gets injured. He could brew potions using the ingredients available in the God of War world, if possible. Harry could also teach Atreus some basic magic, like how to levitate objects. This would give Atreus an edge in combat. And when they are facing a really powerful enemy, Harry could use powerful spells like the Cruciatus Curse (although it's an Unforgivable Curse, but in a life - or - death situation in a different world, who knows) to defeat the enemy and save Atreus.
One popular 'Harry Potter saves Hermione' fanfiction is 'The Rescue in the Forbidden Forest'. In this story, Harry uses his skills and loyalty to save Hermione from a dark creature that lurks there.
One great 'Dobby Saves Harry Potter' fanfiction is 'Dobby's Heroic Deeds' on FanFiction.net. It really focuses on Dobby's unique magic and his unwavering loyalty to Harry. Dobby uses his house - elf magic in creative ways to get Harry out of tricky situations that the original books might not have explored in as much detail.
There's a fanfiction titled 'Atreus and Angrboda: A New Adventure'. In this one, they embark on a journey to discover a hidden realm. It's full of exciting encounters and the development of their characters, especially how their friendship evolves during the adventure.
One popular Atreus and Calliope fanfiction is 'The Adventures of Atreus and Calliope'. It focuses on their journey through a magical forest, facing various challenges together and strengthening their bond. Another one might be 'Atreus and Calliope: A New Beginning' which delves into how they start a new chapter in their lives after a major event in their world.
One place to look for such fanfiction could be Archive of Our Own (AO3). Just search for 'fem harry potter saves tony stark' on their site and you'll likely find a variety of stories. However, I can't specifically recommend a particular one without knowing more about your preferences in terms of writing style, plot elements, etc.
One popular 'harry saves draco fanfiction' is 'The Green Light'. In this story, Harry discovers Draco in a dangerous situation in the Forbidden Forest and uses his magic to save him. It's a great read for those who like the idea of their dynamic changing from rivalry to something more.
There are many great 'Blaise Saves Harry' fanfictions out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Blaise Saves Harry' in the search bar, and you'll likely find a variety of stories to choose from.
There are many fanfiction platforms where you might find 'fenrir saves harry' stories. Archive of Our Own (AO3) is a great place to start. Just go to the site and use the search bar to type in 'fenrir saves harry'. You'll likely get a list of relevant fanfictions that you can explore.