As soon as William arrived in his room after his visit from Aamon's Temple, he found himself seized by three beautiful girls and kidnapped to the Thousand Beast Domain.
Princess Sidonie had been holding back because she knew that William had urgent things to attend to, but she had reached her limit. Because of this, she decided to take action and invited Ashe and Chiffon to cooperate with him.
Although she was jealous that the pink-haired girl had married William before her, there was nothing she could do about it. The rice had already been cooked, so the only thing she could do was to ensure that the next person that William would marry was her.
For that to happen, she had urged her grandfather, Emperor Leonidas, to publicly announce their wedding and ensure that the Half-Elf wouldn't be able to run away, even if he grew wings!