Izuna Zanshinken is a VN put out by Akatsuki Works Black back in 2011.  It is a super-violent chuunige with a vigilante assassin called Musumi Kotarou at its center.  The game is split into two main parts... the common route and the heroine routes, which are accessed at a click of the mouse (convenient).  Save for the end of each heroine route, choices are mostly a matter of seeing different scenes or the same scenes from another perspective.  Each route is split into chapters, each with a defining incident that (save for a few exceptions) ends with the protagonist executing the criminal in question.  Most of these chapters are extremely emotional (the normal chapters have the client screaming their rage, hate, and sorrow at their loss, save for a few where something horrible happens that just requires that Izuna take action), and there are a lot of deep sociological questions buried in the game relating to the death penalty and the functionality of the law... but that isn't why I'm posting here.  I've already reviewed this game once in the past, so now I'm just going to introduce the main characters to whet the interest of those on the fence.

Musumi Kotarou

Musumi Kotarou is the latest in a long line of vigilante assassins (his father was famous amongst them for having killed over a thousand people during his work).  However, his daily manner is literally mild (lol) and easygoing.  It is only when required by a threat or his work that he switches over to the cold, merciless, and vindictive Hitokiri Izuna.  As Izuna, he dresses in a sort of modified ninja costume, armed with kunai, a pile-bunker style claw gauntlet designed to cause pain before death, and a demonic katana (youtou) Kooumaru.  I'll be straight with you... the difference between his daily self and him as Izuna is pretty startling the first time you run into it (in the prologue), but it seems to be genetic in his line (his father was apparently similar).  His voice, body language, and manner of speech all change between the two.  However, they are merely aspects of the same person, as is evidenced by Kotarou's frequent regrets for the necessity of his work, once the bloody rage passes.

Kuzuryuu Suzuka

The head of the Kuzuryuu Family, the yakuza group that controls the criminal underworld of Yuunagi and Kotarou's mistress.  Having taken her position at a young age (fifteen), her manner tends to be stoic, easier to show anger than concern for others.  However, she is compassionate and loving to those she is closest to.  Unfortunately, her position as the young head of a yakuza family pretty much ensures she'll be unable to have an equal relationship with anyone, and while she accepts this, it doesn't mean that she is happy about it.  She is a really Japanese-style heroine, with a preference for simple old-style Japanese cooking, wearing kimonos, and wearing her black hair long. 

Himekawa Shinobu

Suzuka's attendant and a student of Kotarou's father before his death.  At a very young age, her parents were killed in front of her eyes by thieves who raided their house, and over time her heart was corroded by what is probably PTSD.  Eventually, she asked Kotarou's father to train her, and, after refusing numerous times, he finally gave in.  When working alongside Kotarou she wears a mechanized suit that lets her approach the physical superiority of the Izuna bloodline (the Izuna bloodline heals faster, is stronger, has higher dexterity and agility, and is in general physically superior to the average person, even without training).  The suit contains a blade, a function that lets her launch herself high into the air, and a wire for strangling or capturing enemies.  Shinobu is typical of a lot of emotionally-scarred young fighters in otaku media in that she tends to be a bit over hasty, jumps to conclusions, and is easily blinded by emotion.  Nonetheless, she has the potential to make an excellent Izuna, simply because she grasps the central tenets of the Izuna way quite naturally.  

Agano Hikaru

Hikaru is the androgynous daughter of Detective Agano, a police officer who tends to run across Izuna incidents rather more often than he'd like.  She has a strong sense of justice, but she believes that no crime is so terrible that it needs to be paid for with death.  As a result, she is negative toward Izuna's existence outside her own path.  She is very inquisitive and intelligent, but she is also very tomboyish, indulging in hobbies like playing with a yoyo and wearing boyish clothes.  Once she takes an interest in something or someone, she can't help but want to learn more about them, which can sometimes be a good thing but is more likely to get her in trouble, by the rules and probabilities of a violent VN, lol.

There are other characters in this game, but that covers the main heroines and the protagonist... and it is hard to touch on most of the others without spoiling the game fatally.