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Inuyashiki. 

The story's about a sickly, middle-aged husband and father of two (the titular character, Ichiro Inuyashiki) who's inexplicably hated by his family. He wants to do good-- he lives in an area with a fair amount of crime and wants desperately to do something about it every time-- but the combination of his age and his family's discouraging behavior keeps him from doing anything. After learning he has stomach cancer and sitting in a park for a while trying to both cope and figure out how to tell his family, he and a young man near him both see a bright light and suddenly die-- their bodies destroyed beyond repair in the process. 
However, the forces which accidentally destroyed him-- presumably aliens 
[a common trope in Oku's work]-- decide to try and fix both of them.

Since their bodies have been destroyed beyond repair and all they have to spare are weapons parts, 
both of them come back as highly destructive androids, all of their memories in tact. Now they both have to cope with facing the reality that both of them are dead. Their memories and personalities may be the same, but the people they think they were are dead; they're androids, they aren't people anymore. They both react to this differently. 
Inuyashiki, after momentarily deciding he wants nothing to do with his family (since he's a robot and, therefore, has no reason to care about them, and they kind of hate him), rescues a homeless man from a group of hoodlums who tried to light him on fire. After doing so, realizes he's still a good person, that he still has the same emotions he used to have and, even though he isn't what he used to be, he still cares about people and he's going to use his abilities to help people. The other person, however, Hiro Shishigami, uses his newfound abilities to unleash his psychopathic characteristics on whoever he wants, killing at least 15-people in two weeks (including a family of four in their own home). They meet for the first time since the accident (neither of them recognizing each other) as Inuyashiki comes to the home too late to save the people.

VOLUME 1 TILL 7, english.
https://en.wikipedia.org/wiki/Inuyashiki