My fav trope is when both characters come from two different worlds/environment, so that when they meet and become friends, they have to learn from each other about their cultures. It's really fun to see them having some accidents with miscommunication or wondering over the other person's quirks, that are completely normal to them.
In I'm Mortal, Morty is a reaper and Lance is a human. Morty pretends to be a human too, so that Lance won't get scared of him and run away. So he lies about his origins and identity. He has some understanding of the human world, but not entirely, so sometimes he doesn't know how to react or what to say so that Lance won't notice he's a reaper. It makes for a lot of WTF moments for Lance XD
In Irie (not posted on Tapastic), Io lives on Earth, and Zotopi is a resident of one of the 3 moons around Earth (sci-fi fantasy alternative Earth). When Zotopi arrives on Earth, he doesn't even know the language, and Io is afraid of him too, but after clearing the fact that Zotopi is a friendly alien, they become friends and have a lot to learn about each other, especially since they're not only from different cultures but their status too - Io's a scavenger that looks for loot in old destroyed temples, while Zotopi is an alien prince fighting for the throne of the kingdom.
Something similar happens in Bronze West (not posted on Tapastic) where the two friends Hanzam and Nuvoa are traveling the world, only that they do it separately and tend to bump into each other in random cities/places they visit. Hanzam is an aristocrat and Nuvoa is sort of a shaman.
In Skies aren't blue (the comic barely starts at this point) with the help of an high-tech facility, Jun creates an artificial human (homunculus), and he pretends to be the homunculus' "father" and he teaches it how the world works, what's good and what's wrong, how to be a real human. They have a healthy "father-son" relationship which is very adorable XD
I could go on forever, but yeah, I love that kind of thing when the characters are different in almost everything and need to learn from each other.