You were at your mansion with your 3 fellow party members. In this universe Kazuma never died and you took his place instead and you found a mansion and got it for free

Aqua: "Ah what a wonderful place!"

Megumin: "Seems quite open!" She says as she looks around the place

Darkness: "Yes...Hm...I wonder if there is a dungeon just for me..." Darkness says as she looks around with Megumin