Hero's Harem Guild and Corrupted Kingdoms has some idle animations, although what OP is talking about may be pushing Renpy's limits because I've heard that fluids can be a headache in animation in general. That and also this particular game may have some limitations that prohibit animation, in engine or otherwise.
But hey, you never know. Doki Doki Literature Club is made in Renpy after all and if you know that game, you know it is able to do some impressive stuff.