My theory on Daniel's second body.
First credits to the extreme talented artist u/animaoo for the art on of the first 5 images and there's a 6th image I didn't give because it will make others check animaoo out she has many arts and there's more fanmade comics(short) and the other images are from chapter 608.
Now the theory is that the second body is the original Daniel from a world where he didn't get the second body and well got bullied in J high then graduated went to military and suffered but then someone maybe jinyoung himself or maybe someone who is trying to protect the world from Charles Choi and even tho they/jinyoung himself knows jinyoung/he doesn't want to involve his nephew but he has no choice as Charles Choi won yes he won because there is no one to stop him beside James Lee but I don't see how James can make a plan for this if Charles always keeps an eye on him and without a soul to help James his not getting out of Charles grasp. So sb Daniel or future Daniel gets trained by the person or jinyoung himself because the person or jinyoung knows if Daniel is from the same bloodline as jinyoung then he has potential and they need all the help possible and Daniel trains for multiple years and becomes a top tier as we already see our Daniel didn't even train for more then half a year and is already almost or is a top tier now if so everyone can tell how strong would a Daniel be if he trained multiple years of course multiple years because gun doesn't train him (gun=training genius). So after a grueling years of fighting the heros win but there's nothing to really left to fight for allot of people are gone(maybe Daniel's mom and someone else? And the world is in shambles after Charles choi) to fix this Daniel gets the systems help and goes back in time but what I believe maybe two souls can't exist in the same time/world/time-line maybe because they are the same person and same body not different bodies and hence why future Daniel only appears to motivate our Daniel. In the images I gave there are screenshot of chapter 608 which supports the theory future Daniel knew vasco everyone knew him in J high but Daniel dislikes him because vasco never helped him couldn't help him? Something like that and how future Daniel doesn't know jay. And how sb Daniel has all the copy's that doesn't make sense but it does because his the future version that overcame all the things thrown at him. Now the reason why sb Daniel has no mastery is that our Daniel canvt use that sb has all mastery and I believe mastery is more mental line how James said 'figured out how to use strength' against everyone's favorite six fingered king. I believe our Daniel just needs to awaken mastery and sb has it all and path the reason the 5 senses bath didnvt work is maybe because of how very very different experience sb lived compared to out Daniel the paths are different like sb daniel has the same path as jinyoung. Oh maybe Daniel's dad somehow don't ask but somehow got Daniel's mom the god realm and it cause her to get the ability to get pregnant and the reason for Daniel having the ability to quickly heal from injuries and it would explain how our goat little Daniel will survive has he has 50%? Of the god realm in him and yes both Daniel heal fast from injuries.