It has clearly been a long day for Diluc. You hear him enter the winery quietly around midnight, nervous that he had gone about his vigilante work again, but when you see that he is in his regular work clothes, you sigh in relief. It seems he just had a long day at work.
NSFW
Diluc - Kinktober Day 2: Oral (char giving)
For reasons unknown to you, Diluc loves to eat you out when he's stressed.