You got megumin pantie after a event with her if i remember well (it's chomsuke who gave it to you in exchange of a fish) but i could say a mistake it's been a while i have them in my inventory 😂😂😂 (kazuma need to wash them with Rem one's too XD)
And i think it's the only panties you can get..... unless i'm missing a secret pantie steal or idk 👀