Taking these panels into consideration and what we know so far, Sangwoo’s mom tried to kill him. The reason probably being that he killed his dad and she couldn’t forgive him for that.
Afterwards, she decided to completely turn her back on Sangwoo resulting in him being extremely resentful towards her. Maybe those words Sangwoo heard ‘You’re going to die a painful death’ is what his mom said to him before dying.
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