Overlord II

Once Juno becomes your mistress, go to your private quarters. On the left side of the room there should be a place where you customize your tower. Simply buy all of the things that say "Juno" in front of them. (It totals to around 1000 gold) Once you have them all it triggers a cutscene where you are invited to some "fondue."

This achievement is unlocked in the Private Quarters in Netherworld Tower, there you will have 2 important places to go, where the Mistresses are in a long corridor and you must press to make Juno your first Mistress, and to the right of the corridor there is the room decorations where you must buy all things after making Juno your first mistress, after buying all things there will be a scene and then at the end the achievement will be unlocked.