ROY MUSTANG AND DEATH THE KID!
Let me explain why these two. Death the Kid's introduction was...odd. There's no clear explanation such as background of his mother...skills...or his well...childhood.
Roy due to his past. Why did he join the army? How did he meet his friends? And how did he get his powers? Any FMA fan would love his backstory.
Honorable Mentions: WE WANT TO KNOW THEIR PAST!!!!
Hellsing- Alucard
Noragami- Yato
Casshern Sins- Casshern
Black Buttler- Sebastian
Rwby- Uncle Qrow
Tagging @invinsybll @BlackOutZJ @hikaymm