I thought the same. he has to be the god figure. Since flute is broken and they go back and forth in both worlds, balance is broken so  I guess he is there to restore things + guide them. 

I was thinking that also. 

After watching episode 11 I have more information/thoughts about this boy.

Like you all have mentioned, I also think he is the God figure in the drama.

From episode 11 we saw him talking to Luna, she mentioned the red string attached to his Yo Yo and I remembered the Kabbalah Red String, which is a red string that protects us from the third eye. (I think these may be related but I'm not sure), even if my theory is incorrect, due to the Red string being mentioned and even zoomed into, it is definitely important and explains more about the boy. Red string symbolises, protection (This may connect the how we believe the boy is the god figure in this drama), faith, good luck, strength and connection(the two worlds?).

Towards the end of the episode he comes to save Tae Eul and says 'Warn people of danger and defeat the enemy', which I think links to the theory of the red string which is 'protection', as we mentioned before he definitely seems to be the 'God' character, there to guide our main leads and restore the peace. 

The boy also said 'There is only one of me', which could either mean that his other self was killed or he is in fact the only one of himself, making him unique to everyone else in the two worlds (also hinting to him perhaps being the God character).

I hope to hear what you all think :)