Okay so basically in this story everyone has special powers and a way to get them is through these certain requirements 

You must die on August 15 with a partner

When dead, they will enter the heat haze

In the world one will be given the power and will be able to return to the living world and the other remains trapped in the daze

So basically after Jin's mother died, his father wanted to find a way to get into the haze and bring his wife back. But in the requirements you need a pair so one day he met Jin's friends and decided to use them. Jin shocked and hurt by this revelation tried to enter the haze so he would be able to get the power to stop his father and protect his siblings and friends, but he forgot the requirement of needing a partner so he died. 

So after he died, the main goal or wish was for him protecting his siblings so that is why in the end he asked if he was a good hyung.

That's the explanation :3 anyways a hugeeee thanks for reading and I'm going to take a nap. Byeee~