• Coalfang: Like fire & water; Rain & Coal are polar opposites in the best of ways; which led to them being the best & closest friends they've ever had in each other's lives. They fill each other's blind spots, cover for each other's flaws, bring out the best in each other; & are also both highly protective & supportive of each other. For better & for worse, they trust each other with their lives; & would willingly die for the other if it came down to it. They've known each other since they were kids; & their friendship's been growing strong ever since. (They both thought they might've had crushes on each other at some point, but then Rain figured out he was aroace, loveless, & romance-repulsed, while Coal had realised he might be bisexual (also that he was a trans dude) & the attraction he felt towards others while experimenting with his identity in those early days didn't feel like what he felt with Rain, so they talked it out & both agreed that they preferred each other as besties, anyway.)
  
    Nowadays, Coal sees Raintail as his cute little brother, ...despite Rain only being younger than him by about one year, & Coal being shorter in height. He's very affectionate towards Rain, both physically & emotionally- standing on his tippy-toes to ruffle his head-fur, pulling him by the sleeve when he wants to show him something, leaning over his shoulder, hugging, etc. He rants & rambles to him about whatever topic he finds interesting; & lights up like a Christmas tree on the rare occasions that Rain decides to ramble back. But as they've gotten older & he's gotten more aware of Rain's self-deprecating behaviour... well, it's hard for Coal not to worry; even if he'd probably ought to be a bit less... intense about helping him & gentler with how he tries to approach the subject. Coalfang is very ride-or-die when it comes to Rain & often just does things on his behalf that he thinks would help, without actually asking Raintail if that's what he wants. ...Which leads to Raintail retreating further in his own shell out of guilt, because he's worried about making Coal worried & escalating the situation further.
  
    Meanwhile, Raintail greatly appreciates having Coalfang in his life; so much so that he puts him on a bit of a pedestal, seeing him as infallible & invincible. ...Which unintentionally places pressure on Coal as the 'strong one' of the two. He cares deeply for him, though shows it in more subtler ways; & often ways that mirror how Coal interacts with him. Hearing Coal ramble about his interests always made Rain feel better, so when he notices Coal being upset, Rain'll try to do the same for him; rambling about whatever Rain finds interesting, to distract & cheer him up. Other than that, he's usually just happy to follow his friend's lead. He couldn't bear bothering his dear friend with his own dumb ideas- it's a miracle he even has a friend in the first place, isn't it?
  
    They're both just trying to help each other, but between Coal's fiery compassion & Rain's endless guilt, neither of them realise they're not obligated to always do so, or that it's okay to accept support from the other person, instead of only giving it- or even just step back & say "no". Friendship is supposed to be a two-way street & these two are crashing Ferraris into each other's metaphorical houses.

• Windmark: Wind & Rain were introduced to each other through Coalfang, back when Wind & Coal were still dating. While they're not as close, having spent less time with each other, they do appreciate each other's more calm & quiet personalities, meshing together like snow & water. They're kind of vaguely friends? They consider each other as such & go out of their way to talk to each other; but despite the presence of an emotional connection, the way they actually interact with each other is more akin to acquaintance-you-barely-know. There's a huge fundamental layer of misunderstanding between Rain & Wind, due to both them having a shared inability to open up about their feelings & communicate properly. 

  Wind does actually care about Rain, but also kind of lowkey thinks of him as a blithering nobody- both in the "somewhat endearing, sweet younger friend that's like a kid" way, as well as the "can you go away, you're so genuinely annoying & stupid" way. She doesn't know how to actually voice this, though; so she just falls back on what she usually does when she cares about someone but doesn't want to: tough love. She's as harsh as she always is, though makes an effort to cut back on her snark. ...Not like that's noticeable to Rain, though.

  Meanwhile, Rain just does not register the fact that Windmark considers him her friend, wholeheartedly believing that she just straight-up dislikes him. He can't help but care about her, though, even though he believes it isn't returned. He sees through her cold demeanour & just sees another fellow lonely soul; but stays averse from getting too touchy-feely, both out of respect for her boundaries, & because he worries he'd just make the whole situation worse. He never says a word in retaliation to her snark- believing he deserves the insulting, anyway, & being the punching bag for Wind to let out her own feelings seems like the least he could do. (THIS IS NOT HEALTHY FOR EITHER OF THEM. I DO NOT CONDONE THIS)