I think you said it : circumstances. None of my chars has spontaneous sexual attraction towards creatures, some are even pure straight hetero not knowing anything aside of it. However, some of them would be willing to bargain it (just as Selune) in exchange of something they see as even more valuable, some of them could get drunk/drugged, and some of them could be forced into non consensual relations.

So, circumstances !

As for Kallista, since the episode with BIkki's tribe, one could have thought she hadn't anything against rieklings at least.

I voted for 3 & Dog/Wolf, but I'll be damned if my wicked mind ever produces any sensible ideas for storytelling. I know you specifically asked for good ideas, but here are some lousy ones nonetheless:

1. A good old "man's best friend" scenario - a reward for a gentle and loyal creature. Might not be too sensible portraying loyalty with the short time span of a single comic, though. 

2. Similar - a Roscoe-to-the-rescue (with a very appreciative lady) story. Has been done before, so it's probably a bit cliche at this point.

3. An injured pup (hunter's bear trap?) being tended to.

Now I feel the need to apologize for having made anyone read those!

I think you said it : circumstances. None of my chars has spontaneous sexual attraction towards creatures, some are even pure straight hetero not knowing anything aside of it. However, some of them would be willing to bargain it (just as Selune) in exchange of something they see as even more valuable, some of them could get drunk/drugged, and some of them could be forced into non consensual relations.

 

So, circumstances !

 

As for Kallista, since the episode with BIkki's tribe, one could have thought she hadn't anything against rieklings at least.

Yeah, circumstance is pretty much the main thing. I was mostly referring to situations where a character would willingly choose to break their own rules. Non-con wouldn't really count, and getting drunk and making a bad decision is sort of a hazy area.

As for Kallista and Rieklings, it's mostly just Bikki she likes. He's a bit stupid, but she thinks he's adorable, and the way he acts towards her when he's horny is a weird sort of turn-on for her. She wouldn't fuck just any Riekling and doesn't find them attractive in general. Really, beyond Bikki, she's never felt any sort of sexual attraction to a creature of any kind before, making Bikki, and Rieklings by extension, an exception to the rule.

Consensual option #3 w/ wolf idea:

Kallista happens upon and pack of wolves fighting with a bear (or similar). The bear wins, killing the wolves and then leaving (or maybe dying itself from its own injuries, or from Kallista killing it). Once the bear is gone one way or another, Kallista hears whimpers coming from one of the wolves that wasn't quite killed. Taking pity on the creatures' pain, she field-dresses its wound(s) and then carries it back home or something to properly nurse it back to health. At some point during this recovery period, she notices it get erect while tending to it on several occasions.

Neither act immediately (the wolf because its injured, and Kallista both because its injured and because she's not sure), but the curiosity lingers and their companionship grows as they spend more time together and its health gradually returns. Then, once it's fully healed, she lets it have a go with her before she lets it leave/sends it back into the wild (or, my personal preference, it becomes a new pet/companion for her since it no longer has a pack of its own. then they can do it more on occasion if/when the mood strikes).

Of course, I'm all in favor of her having some fun with Bikki, too (maybe both of these scenarios could happen at some point?). But for the purposes of this poll I voted for the wolf option.

 

Yeah, circumstance is pretty much the main thing. I was mostly referring to situations where a character would willingly choose to break their own rules. Non-con wouldn't really count, and getting drunk and making a bad decision is sort of a hazy area

Yeah, but historically  non consensual we're the only circumstances it did happen to some of my characters. My girls do accompany me through my games, and one of them, in New Vegas, was abducted and forced to take position under a dog trained for it in front people making money of it. Funny enough she kept the dog afterwards (he was as much a victim as she was in fact), but never again did she had sex with it. 

Another one was almost raped by Falmers. Can't imagine a reason for her to submit willingly to that, unless getting used to them from a long captivity. I believe the mod « things in the dark » allows something like that, but none of my char's have met such extreme circumstances yet. But the « living-with » « getting used to » factor is a powerful catalyser, even IRL, and even among different non human species as it as been witnessed.

As for Kallista and Rieklings, it's mostly just Bikki she likes. He's a bit stupid, but she thinks he's adorable, and the way he acts towards her when he's horny is a weird sort of turn-on for her. She wouldn't fuck just any Riekling and doesn't find them attractive in general. Really, beyond Bikki, she's never felt any sort of sexual attraction to a creature of any kind before, making Bikki, and Rieklings by extension, an exception to the rule.

Well, attraction for the weird or the different  is something that can grow with circumstances it seems. That's a setup. 

One might think about loneliness as well, though I think there must be a kind of attraction to the weird beforehand for it to lead a character (even real persons maybe as well) to bestiality. What is strange to one will be arousing for another, LL members learn to know it. 

Or a natural curiosity. The second born of the Marsoric sister has this trait. The thing is her curiosity already finds an answer with beastmen (khajits and argonians), and the creature should have an interest to it as well for the possibility to arise. So did not happened yet, and may very well not. We come back to circumstances once again it seems.