They remind me so much of Eiden and Yakumo from Nukani
Reirin is totally mary sue character. I'm so dissapointed with keigetsu's character development. The author has many chance to make her matured and changed for real but no they decide to give Reirin to take the spotlight from Keigetsu everytime she can prove her worth. Reason : "because I want to protect keigetsu" Don't give me that bullshit, at this point Reirin is just a control freak and manipulative perfect maiden that befriended a "lowly villainess" that are worse than her. Friend are supposed to walk along with you not do things you can't in your stead everytime.
So basically Brutal: Satsujin Kansatsukan no Kokuhaku (Brutal: confession of an homicide investigator) is an article wrote by a journalist telling about Dan's confession of his murder before he was caught and now is waiting on death row (of course this is not a spoiler since the order to read this series is Trace then Brutal )
After reading trace and brutal I'm convinced that Dan Hiroki is the older version of Okaya Nozomu from Maria no Danzai
Wait the mc sorta looks like Caelus from HSR HELP