I have a bad feeling about all this. Akutsu will return to Earth, and once he gives up being a demon, he won't be able to come back down. And Amane was most likely threatened by Yamada to stay in Hell, something like... "I can blow up Akutsu because he has a bomb" or something like that. They're going to apply to Akutsu what they applied to Rudeus in Mushoku Tensei; Amane is going to give herself completely to him as a farewell and leave... Now it's time to make the foray into Hell, fight the sisters, defeat the butler, and finally be together again. And I have a feeling this is how this manga will end...