Here's the thing. Reapers have numbers as their names because they died and their bodies never were found. So, they bare the number of the date they died. And when they do, they forget all about their past as a human. So, according to this common knowledge of reapers in korean culture, Geumsun probably had some kind of relationship with 704 before he died and became a reaper. Probably while Geumsun was sleeping recovering from his injury, 704 died and Yamma brought him as a reaper. And that's why Geumsun was so shocked when he saw him "for the first time" because they have history but 704 doesn't remember a thing. The only way for a reaper with a number as a name to recover their human memories is to found the location of the corpse.
Here's the thing.
Reapers have numbers as their names because they died and their bodies never were found. So, they bare the number of the date they died. And when they do, they forget all about their past as a human. So, according to this common knowledge of reapers in korean culture, Geumsun probably had some kind of relationship with 704 before he died and became a reaper. Probably while Geumsun was sleeping recovering from his injury, 704 died and Yamma brought him as a reaper. And that's why Geumsun was so shocked when he saw him "for the first time" because they have history but 704 doesn't remember a thing. The only way for a reaper with a number as a name to recover their human memories is to found the location of the corpse.