Gaahh they didn't show his transformation. Apparently it is painful because of the wound
You're right, but without the transformation scene, I don't think manhwa readers will understand how much pain Heesung went through just to get back to his hyung. Maybe they'll mention it next chapter though. I've noticed that they'll sometimes add in details from the novel a little later than in the manhwa.
Is it actually completed at 19 chapter or mangago decide its complete.