Pointless.

Eventually, he too notices the writings on the various rooms and despite he thinks it must be a joke from some bored Avatar, he decides to go to take a look, just in case.
He arrives there while JiHwan and Liang are talking and at first, he completely ignores the kid, just sending a glance at the empty broom closet nearby.
"Abanim...!"
To that word, he freezes and moves his gaze on the child, because he is not wearing his amulet and can tell the boy spoke Korean. Only then he notices that he is wearing a typical hanbok of early Joseon times, his times. "W-what did you... say?" he literally gasps those words, in Korean too.
The child looks down and points at the parchment he handed to Liang that Bang-sul takes away from.his hands without hesitation. He looks at the portrait and the ideograms with wide eyes and getting paler and paler.

He takes a step back and actually runs away from there, to the bathroom. He knows it can't be a joke, no matter how he would like to think otherwise. He feels totally overwhelmed by this, it's the most unexpected and he just can't understand how it can be possible.
He takes another look at that paper... who ever, of who he knows, could be able to write in a, by now, dead language? Who could architect a prank like that, in such a moment? It can't possibly be, it can only be true.
He left a wife behind, with whom he was forced to sleep, although it made him sicker and sicker every time.
He shivers and ends up throwing up. It has a devastating effect on him.

After calming down a little, he washes his mouth, face and hair with the cold water, in hope to regain some control.
"What do I do now?" he mutters to the mirror with a broken voice. He also cried and still cries.
All the sudden, a lipstick starts to fly in front of him and to write in the mirror.
He takes a step back, looks around, but there is nobody he can see. His senses though, can perceive a presence and keeps making him shiver.
'You must go to him' appears on the mirror in red, eastern dolashin.
Bang-sul gasps. "Who are you? What is going on?"
'Go'.

Bang-sul takes a deep breath and tries to fix himself to look a bit less messed before going to meet his son. He doesn't know who the ghost in the bathroom is, but definitely doesn't want to test its patience.
After searching for some minutes, he finds the child in the lounge room and goes to him, without thinking of he'd probably end up petrified at the door.
The boy is sat, he just walks in front of him and crosses his arms on his chest. There are so many questions he has, but decides to start with the one that feels the most appropriate. "Who are you...?" Maybe a 'What's your name' would have been better, but his brain is too spammed by junk thoughts.
The child stands up and, after sending him a quick glance, he bows and kneels, then prostrates himself while saying: "I'm Yi JiHwan, Prince Bokdae, abanim..."
Bang-sul bends on his kneels and forces the boy to kneel up, then gives a careful look at his face. He is human for sure, he is not let likely from Joseon for real, considering his Hanbok and the fact it's real silk... plus the parchment. "How did you..." He interrupts himself as he almost sobs, there. "How did you get here?" he murmurs in a broken tone.
JiHwan gives him another shy glance. "The wizard opened a magic door for me... after you disappeared in the lake."
Bang-sul shuts his eyes at his words. He is not sure yet if he should be glad for this or not, for now he only feels totally panicked. "How old are you?"
"I'm 10 years old, abanim..."
Which perfectly matches, as he traveled back to 10 years after his own 'death'. Considering what his family was like, though, he can't imagine what his child's life could have been, alone with them. "Your... eomanim?" It disgusts him so much to even just mention that woman, but she was still the mother of the child...
JiHwan looks down and shakes his head at the question.
"She is... dead?" Well, in 2019 she is for sure - he thinks.
"Ye, abanim... I've never had the chance to see her..." he murmurs in a cute and sad voice.
Better for you, truly - he thinks, but would never say that outloud, for some reason.
He covers his face with hands and takes a deep breath. "And you... want to be with me?" Probably the most idiot question he could ever ask.
JiHwan looks at him with wide eyes, then moves his gaze to the side. "Ye, abanim..."

His son. His own son. And he abandoned him in that nightmare... it doesn't matter how it wasn't by his own will, he keeps feeling that way.