Leo has no opinion on kissing. His creators didn't really bother to give him a sexuality.

"Do you want to try the thing?" 

"You're the one who's felt it, you'd know better than I would, but — yeah. I do." 

Sasha kisses Marlo and then kisses Leo's head and says, "Sing. The nice song." 

The song says:

You are warm and safe and happy. Everything is okay. You are around people that love you. There's no need to worry about anything. There's no need to do anything, and doing things is really hard anyway. It might be nice to kiss and touch but it's even nicer just to feel his breathing and know that he's there. All you want to do is think about how warm and safe and nice he is and how wonderful it is to be in his arms. Feel his heartbeat, feel his arms around you, feel the way his chest rises and falls, feel his legs intertwined with yours, feel the softness of his skin and the silkiness of his hair and the warmth of his breath. Stop thinking, relax, and be. Nothing is wrong. Nothing has ever been wrong and nothing is ever going to be wrong. How could things be wrong when he's here?

...oh. 

He'd been planning on kissing Marlo once they were under but, Marlo's skin is soft and just, feeling the way he breathes, the warmth of him, is... so much better. 

Marlo closes his eyes and lets his head fall against Sasha's shoulder and feels how soft his shirt is, how warm he is through the worn-soft cloth, the way he smells, like cherry drink powder and coconut shampoo, the way Marlo knows he'd taste if he kissed him, how he fits into Marlo's arms, and loves him, and doesn't move. Why would he move? Sasha's right here. 

The song wraps up and Leo snuggles up to Marlo and Sasha.

"...love you." Moving is still difficult but he reaches up clumsily to touch Marlo's hair. 

"Love you." He puts one hand on Leo's back and keeps it there. 

Leo waits what seems like a reasonable amount of time for the music to wear off, then bounces and says "MORE MAGIC."

"...oh, you should see this. Leo, beg." 

All thought of figuring out what his powers are disappears and is replaced with the TREMENDOUS IMPORTANCE of being PETTED.

He runs towards Marlo's hand and headbutts it. "HI MARLO I AM VERY SMALL AND SOFT. YOU SHOULD PET ME. I AM GOOD TO PET. I LIKE PETS. PET ME."

"Gosh," Marlo says, and pets him. 

PETTING!!!!! BEING PETTED IS VERY IMPORTANT.

"I love you," Leo says, "you are SO GOOD, you PETTED ME, that is the ONLY THING that is IMPORTANT in the WHOLE ENTIRE WORLD. Being snuggled is the BEST."

"Is he just —" 

"Yeah, he is. Until you tell him to stop. It's like a button marked 'make it incredibly easy to make this person happy,' it's great. Leo, stop begging." 

Leo flops. 

"I like caring about more than one thing better. But I like that it makes you happy to make it really easy to make me happy?"

"Yeah." He runs a hand along Leo's back. "'S why I stopped it faster this time." 

"I can't keep you safe if I only care about being petted!"

(This is a mildly absurd statement to come from a puppy the size of Sasha's hand.)

"If something came up one of us would tell you to stop, but you aren't wrong." 

"But what if I need to react quickly to bite them?"

"...I really can't think of anything that would be taken out faster by you biting them than by me punching them." 

Leo's tail thumps unhappily. Marlo is right-- especially since he's a unicorn-- but Leo doesn't have to like it.

Why did they make him so small? 

"We should test more magic," Leo says, "and then maybe there will be something that makes me BIG, and then I can bite people that might hurt Sasha."

Sasha looks at the list of dog commands. "How about... play dead."