Edit:
Its unlocked by completing the level with time to spare.
The bellow comment is not accurate for this game.
By finding the animations in game, There are two that can be found in town when doing lewd work. Then the rest can be found during adventures.
Some of them need to be found during lewd adventures, the lewd adventure shows up when the horny bar is maxed out and its an adventure with a heart. Completing it will let you select if you want the lose animation or the win.
Then there is also one with the demon queen. For those animations you need to reach her and win or lose.
Keep in mind that if you have the dildo artifact equipped. You can unlock additional animations for some of the lewd adventures.