SAI means “again” in Japanese, like the prefix "re-". In this 3rd volume of Heaven and Demon, Aoki and Tengoku starts dating and slowly deepens their relationship. But one day, when Aoki is talking with his friend on speakerphone while cooking, he brings up what Aoki said some time ago that he had no plans to marry his current partner. Tengoku hears but says nothing about it. When Tengoku leaves after the dinner, Aoki walks together to the station with a slight feeling of uneasiness. They kiss on the way, on the dark, lonely street at night. When Aoki notices someone passing by see them kissing, he almost unintentionally says “...This sucks”. Now Tengoku suddenly changes his tune and walks away, leaving Aoki alone and perplexed. Why does Tengoku leave like that? Their good relationship now seems to be in crisis...
