I was proposed to by the Final Boss. Original Novel:Novelpia, Onestory, Nate, KyoboBook, KakaoPage Official English:Genesis Studio, Novelpia

Extra-dimensional beings known as the Nova have invaded our garden world, hellbent on wiping humanity off the face of the planet. The only hope is a specialized force of genetically engineered female Pandora...

From MangaHelpers: Seven years ago, Yuto's older sister vanished through a mysterious door, leaving him with only a necklace. Now he has once again seen that same door, and watched two mysterious girls (Saya...