creative writing - How do I convey that a relationship is platonic?

I've been toying around with the idea of writing a novel. The story revolves around two characters, one male and one female, and the perspective will shift between them.

One of the central ideas of the story is that the two characters couldn't be any more different. They have different sets of talents, different world views, different ways of handling crises. Yet despite all that sets them apart, they're the best of friends. Nobody, including the two of them, can quite put into words why their friendship works as well as it does, but they're nonetheless inseparable.

Here's the catch: This is not a love story. Both consider the other a close friend, but nothing more. It's not something they've ever considered, and their relationship won't ever become anything more than what it is. Unfortunately, every introduction for the two of them that I've come up with invariably feels like a cliched setup for a cheesy romance.

I could directly call out the fact that they don't view each other in a romantic light, but that feels sloppy, and doesn't resonate very well. I'd rather show that they're just friends, rather than resort to directly summarizing how they feel about each other. I also don't want to introduce a different love interest for either one of them. In their eyes, they have each other, and that's about it.

What's the best way for me to introduce their relationship, and not overtly hint at a future romance?

Answer

I agree that establishing the platonic nature of the relationship is important. There are a number of ways to approach it, as in David Doyle's answer.

But additionally, I wanted to point out a couple key things to consider:

Be aware that even if you gently indicate that the relationship is platonic, many readers will still be watching for signs that there's a potential relationship waiting to blossom. That is the nature of literature - many of humanity's stories revolve around a romance story or contain one, thus readers will have a strong tendency to suspect romance. They may even start to hold out hope.

Therefore, if you don't want that tension to develop and the reader's hopes end up unfulfilled, it's probably best to establish a clear reason why it isn't romantic and never will become one. There are numerous non-cheesy ways to say that someone loves someone like a sibling.

Secondly, in your question you state "not something they've ever considered," when perhaps that is part of the problem you're running into. The "romantic feelings haven't ever been considered" scenario is actually at the root of numerous love stories: "when X pauses to truly consider his feelings for Y for the first time, he finally realizes his love for her." It's almost a trope.

But if instead they have considered it, and then come to a clear conclusion that they have no romantic interests for a good reason, it is going to be more plausible that a romance isn't likely to develop. Then readers will be less tempted to draw romantic tension into it.