
I think I can understand why Hyeongoh says "I'm fine" and "I'm okay" all the time. It's to keep him sane—to keep him alive. I'm sure he wants to die, but has some hope that all will be okay.
However, for those saying they "can't stand the cripple because of his stubbornness," that's really cruel. You can't judge people on the way they act. Everyone has their own circumstances, their own thoughts, their own trials they believe they have to overcome on their own. For some, those bullies are just cruel and evil, while in some cases there are other mean people who act out because of their past and they don't know how to be a decent person.
Don't hate me! These are just my thoughts on the matter. In fact, I really enjoy this story. <3 (I'm only on chapter 11 right now, so please don't spoil anything if you decide to comment!)

Absolutely agreed! No worries!

I'm not confused.

Yeah. It's not explained very well in the writing itself, but the story line is clear to me.
Ran is the eldest, Miki is the second eldest and Sue is the youngest son. Ran is willing to do anything for his brothers, which means that he's willing to hold back his feelings for Ai (Miki's best friend) because he believed Miki was in love with Ai.
Ran sells himself to get more money to pay for food bills and living expenses, aside from his job as a hotel clerk. His red hair is disliked, but when the scar on his chest is added to it, people basically think Ran is disgusting (which explains why the "customer" threw the extra money at Ran and left). Ai found out that Ran was selling himself and basically threatened to blackmail/attack him (sexually) if he didn't show Ai his scar.
The scar came from protecting Miki during an incident when they were children. Ran had been jealous of Miki's good looks (blond with blue eyes), so he left his little brother alone at the park and went home. He was sent back and saw the man holding a knife, then threw himself in front of Miki just in time. Ai was caught up in the incident, which is why he got that scar on his right eyebrow.
Ai had fallen in love with him at that moment, but he wasn't sure that Ran was the one because Ran didn't like people seeing his scar. So Ran said it was okay to attack him, and Ai ripped open his shirt to see the scar and confessed his feelings. Tada, they have sex and afterwards Ran feels guilty, because of his misunderstanding of Miki's feelings.
And at the end of the chapter, we find out that (unsurprisingly) Miki has feelings towards Ran, not Ai. Miki punched Ran only because he was upset that his older brother didn't notice his feelings.
I hope that helped. :3
It's not cliche and the art is very well-done. It gives off a dark psychological sense, but it plays well into the "mysterious amnesiac turned detective" story line.