Descendents of Darkness (Yami no Matsuei) #4 by Yoko Matsushita
Amazon link: Descendents of Darkness #4
This starts off as one of the lighters stories in the series. There’s plenty of humor and the characters are very much themselves, but it’s a view into their lives at the office as opposed to in the field. The final story is more in keeping with the darkness of the rest of the series. There’s murder and mayhem and outright discussions of sexuality. It’s well worth the read, but definitely start at the beginning of the series.