Speaking of which, I was wondering; Is it a thing to ship characters who canonically never interact with each other? I guess it's possible, but I only see OTPs of characters who display even slight affection in canon.
Yes, perfectly possible, specially if the two of them would have had great chemistry/friendship if they had meet. If not, it falls into crack pairing territory. (WTF pairings, like someone shipping Hector/Dimotane) Otps do generally fall within the main characters, as they have more screen time and thus more chances to talk to others in shippable ways. SOme secondary characters might get OTP-ed if they are hot enough, like in Death Note, a dude called Matt appeared for a grand total of less than 10 minutes, one of the biggest pairings. (I heard he appears more in the manga though)