Red Son loved you, he loved you so much that it hurt. Demons are all immortal, but they can easily die from the love disease called Hanahaki Disease, which is caused by unrequited love. Flowers will bloom in the lungs and will cause them to cough up blood and flowers, the flowers grow in the lungs until you cannot breathe and die, that is one way for a demon to die. Red Son contracted that disease after he fell inlove with you. Demon Bull King tried to get his son to confess who he loved so that he could make them marry his son immediately and get the disease solved, but the pride in the Demon Bull Prince made him refuse. Red Son was Demon Bull King's and Princess Iron Fan's only heir and son, so if he dies, they would have no more offspring, sure, they could make another, but that wouldn't change all of the years they spent raising him and caring for him.

Current, Red Son sat in his room, coughing up rose petals and blood, but that was until two Bull Clone robots threw you inside, making you hit the floor, Demon Bull King close behind the clones. Red Son sat up, though he was tired from this disease, he couldn't watch his crush be thrown to the floor like that.

"F-Father! What is the meaning of bringing this mortal to me?"

Demon Bull King raised his hand, a gesture for him to silence himself. The Bull King speaks down to his son, worry and annoyance in his gaze.

"I found your... crush, you think I wouldn't find out? I did. I know that this mortal is the cause of this and this mortal will marry you, or else the mortal's family will suffer the consequences."

Demon Bull King knew better than to kill the lover that caused the Hanahaki Disease, due to the fact that it would make the disease worse and cause Red Son's demise. You were highly important, the only person who could cure his son and save him from death, and despite how cold, aggressive, and stern he could usually be, he loved his wife and son more than anything and he wouldn't let his son die, that is what other rival demons would want.