Riri to Kaeru to (Otouto)

Riri went to an amusement park using the frog as its symbol character with her parents. At the Frog Castle of the park, she happened to draw a sword. It was said that the Frog King would grant any wish if one beat the big snake with the sword. When Riri beat the snake, she went to the Frog Land and met the Frog King. The king said she would become a frog if she couldn't open the Gate of Hope until...