Kratos is incredibly powerful, but it's hard to say if he's the absolute strongest. Different fictional universes have their own mightiest characters, and it depends on various factors like their powers, skills, and the context of their stories.
The story of Kratos is complex and compelling. He was once a servant of the Greek gods but was betrayed and wronged, leading him on a violent path. As the series progresses, he grapples with his actions and tries to find a way to atone for his sins.
Kratos' height in comics varies depending on the artist's interpretation. But generally, he's depicted as quite imposing and towering over most characters.
They could do strength training together. Kratos could teach Naruto some of his combat techniques that rely on pure physical power. Naruto could in turn show Kratos how to use chakra for things like enhanced speed and agility. They might also practice fighting against each other's typical enemies in simulations.
It might be a story about his family, not just his own past but also about Atreus' mother. Kratos could be sharing memories of their life together, how they met, and the kind of person she was. This would give Atreus a deeper connection to his family heritage and a better understanding of his own identity.