From the very start to the end this is yet another example of the Korean way of making action movies.
On one hand, a lot of bloodshed and fighting (not to be misunderstood, the action moments are very well chosen) and on the other hand touching moments and a gentle exploration of the characters. For me this is quite an interesting recipe and a breath of fresh air from the clichés of the "classical" action movies.
Enough generalizing. Just thing about it: how would you live, if every morning you would punch your card and than head into an office in which you would get an assassination mission. Business as usual, right ? Well, have you thought about it ? Good. Now let's guess. What would a man with no family and the desire to head another way. A man who had his taste of blood, who satisfied his inner need for violence. Wouldn't he try to make a connection with the real, human world ? Wouldn't he try to befriend someone trustworthy ? Well, if you do want answers to these questions, watch this VERY interesting movie. One more thing. Hope you're not a vegetarian...