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Sung Su-Ho is Jin-Woo and Cha Hae-In's son who was introduced in the extra chapters of the series.
In the novel, he was described as a boy with a seemingly right body for a middle schooler, not too tall nor short for a boy of his age. His eyes, when meeting his enemies, shines dark blue like his father.
Su-Ho have a fair share of his father's attitude, having no interest in other things that doesn't literally pumps his blood. He sees the school as a boring place and casually defeats any bullies if they would ever come his way. He shows intense desire to fight against his father, whom as always, defeats him. He is shown to have familial feelings for each Shadow Monsters, especially to Beru.
Su-Ho started showing his power at age of six months, shocking his mom,Cha Hae-In . Later his friends were also afraid to come near him,due to exposure of Power of Death. So Sung Jin-Woo, sealed his memory and powers for a while,till he learns to control it. Later, Su-Ho is seen in high school, where took care of a bully, comes back to class and once class ended, he looked back to the school grounds and thought how boring it was. He then hurriedly fixed his things as he doesn't like to make his mother mad and was about to leave the room but he wasn't able to do so. Instead, a dark circle starting from a small figure of a ball to a huge one.
The gate before Su-Ho gave him an intense feeling of longing as if he was asking for it. He entered the place out of curiosity and met many monsters and fought them by himself. Monsters which range from Blood-Red Commander Igrit, Ants, the crying Beru and many more.
After which he received the information that he leveled up to 99, Su-Ho wakes up from his slumber in his table. In front of him was his classmate which was waiting for him to wake up. As gratitude, he invited her to dinner at home.
Meanwhile, looking not faraway, Jin-Woo was pleased with the test he gave to his son with Igrit and Beru (who is crying while looking at Su-Ho's drawing).
Su-Ho was exceptional even for a half-human, half spirit, as what Igrit commented that Su-Ho isn't only strong because of the powers that he is slowly receiving from Jin-Woo but because he was a son from two strong beings, a monarch and an S-Rank Hunter.
Jin-Woo also revealed that the tests he was giving his son is for him to slowly integrate the powers of Shadow Monarch to his son, hinting that there is an upcoming enemy that maybe his son will have to fight.