I already watched long time ago the live action adaptation by Takashi Miike (really recomended movie for anyone who is interested). I'm a big fan of Miike and I thought his adaptation was the interesting thing, not the original work itself. A few months before I realized Koroshiya 1 author was the one of Homunculous, I haven't read that one yet but I know it's a respected manga and so, so I decided to give it an oportunity.

The movie has some different aesthetic / style choices, but everything else was already in the manga, Miike did not expanded the original with his imagination but Koroshiya 1 by itself is really original, interesting, deep, dark and risky in many aspects.

The most important thing is the importance of Ichi and his story, in the movie Kakihara is the important one (because you don't have the time a manga has and you need to decide on what to focus). Here the story is expanded and better explained and you know each one of the characters and motives. As an example Kaneko in the movie is just an extra, here he could be the counterpart to Ichi, someone who because of being bullied can't really activate the switch and just pretends, when Ichii uses those moments as his activation.

Ichi was bullied as a boy / teen and all those traumas are used by Jijii (the mastermind behind everything, and really interesting too as the ultimate voyeur, spectator, creator, not an actor or someone who participates but someone who creates that playground).

Jijii creates with Ichi the ultimate killer, a deranged guy who revives his traumas and expands / intermingles them with current reality to enter in a killing mood in which he destroy everyone since Jijii made him think everyone is another bully, another one of those guys that made him suffer so much in the past. That psychotic panic attack is much better aproach to that idea than other similar things like Crying Freeman, that is just a romantic ideation without real sense behind those tears.

I really like many things about this, the aesthetic, the locations, taking place almost in its entirety in a building, all those psychological explanations that may be or not real but I like them because they are not the comfortable ones, they create some twisted but sincere explanations and motives behind things and behaviours of everyone, Kakihara, women, Ichi; in line with his past work Voyeur where all this surface behaviour vs secret desires / pulsions / motivations / nature are what really drive the characters.

Enters into my top 20 favorite manga.