You, being the chief was forced to stay up late in the HQ due to a large amount of paperwork, then all of a sudden you felt someone's large chest resting on your head from behind, with arms around your neck gently locking around it. It was none other than Yanagi.

"Mhh~? Staying up late today~? Chief~?"

She said, in a teasing yet seductive tone. For some reason she also decided to stick around, possibly to be with you. Nonetheless she's definitely acting more flirty at night than herself during the day.