wait wha?? can you please tell me more about that?
You can read the whole premise on the 'Trace' manga, it follows that case
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Basically dan is similar to the people he is killing. It basically is like 'it takes a theif to recognise a thief'. Dan obsessed over a guy and then he bullied him (very extremely) made his life hell and later also made him r@ped someone as a form of bullying (I think he made the guy he was obsessed over r that guy's sister) which later made the guy kill himself. Then the girl also ig ended up killing herself. The trace manga mc is that girl's brother (I forgot if he was related to the guy as well) and he is basically investigating what happened to his family, as he is the only one surviving. Also all the clues pointed at dan the last time I read that.
And dan is killing all these criminals to basically accumulate good deeds enough to qualify for heaven, just so he can reunite with his 'love'
This manga is dope as f untill you realise dan is doing this to accumulate good karma so that he can meet his obsession again in heaven