Based on the erotic doujin game by Remtairy (レムテイリー).

The protagonist, Meltys, is a non virgin, single princess who fools around all day every day. She stays outside of the castle all night and takes naps in her room in the middle of the day. That was the setting of Meltys's peaceful life in the Kingdom of Rothstein. However one day, it was suddenly invaded by Monsters! Those Monsters were from the Underground Empire of Grolido. They destroyed Castle Rothstein and wiped out all their troops. Even all of Meltys's big titty older sisters were captured...

"Well, I'll like somehow fix everything!"

Despite being outmatched in a dangerous situation, Meltys sets out on her quest with her typical upbeat demeanor.
This is the story of the beginning of a light hearted journey that can quickly turn into a very erotic adventure...

(Source: DLsite English)