
basically back in the research facility, Rimbaud got pregnant i believe after bai chuin got taken away(to be later sold to a fight club) and the doctors found out and decided to forcefully take out the child (which was in shape of a pearl) from his private part (hence you see the scar under his fins which bai chuiun thought it was the result of being raped by other alphas). Poor Rimbaud was crying in pain and begging the doctors to not take his child away.
After the pearl was removed, the freaking doctor accidentally dropped the pearl to the floor which killed the child leaving a crack on the pearl.
Years later after Rimbaud escaped, he wanted to go to the same research facility and take revenge but also retrieve the broken pearl that the doctors kept but that didn’t happen bc of him being captured by traffickers and bai chuin saving him (everything that happen in chapter 1).

Actually after the their kid died, the pearl was kept and been given to an experimental subject named “undead” as his slave. Undead has the power to revive anyone that died and used them to do his deeds. Undead revive their child (pearl) and made him attack his parents. The sad part is that pearl had the mentality of a fetus not knowing why he existed and he begged Rimbaud during his fights with him asking rimaud“who he is?” Or “what am I?”.
Rimbaud didn’t even want to fight him (and in the novel he hesitated a lot) and just want to bring his song back into the ocean to bury him.

No. After fighting with Rimbaud a couple of times he slowly realize that what’s he’s been doing is wrong and he resisted the control of the undead.
There was a part in the story where Rimbaud told him that he’s his mother and that bai chuin is his father and he called bai chuin papa in mermaid language. And they all shared a warm hug.
But pearl died due to the fact he sacrificed himself by dying together with undead saving the world. The saddest part is that after a certain somone’s death, all Rimbaud had left was his son that he hugged for one last time before he pushed him away to die with undead.
Spoiler
Can anyone tell me more about their child?