I asked a friend who's a 10x Python engineer for some help getting you an answer here. He recommends:
I don't think there are any robust ORMs for asyncio. There's Gino but I haven't evaluated it. I would honestly use an asyncio SQL connector, manually write the request, and implement a mapping layer myself.
Asyncio is still a bit weird a lot of libraries hack compatibility layers onto it. It's probably better to use aiohttp alone instead of putting Tornado on top of it.
ORMs can be painful and newly created ones on new platforms are even more painful.
Hope that helps!