Also can anyone tell me how doctor health is got worse?? I don't remember anymore

because the doctor use alot of magic to take back kouichi into the isekai again. the reason why he hasn't healed yet is because the current king of titan is sick. the thing is if king got sick - people cant get alot of magic power because the king have a duty to share his magic power to their people. that is why they are in such a rush to find the new king

Ohhh... thankyou...now that kouichi complete thst egg task they should get married and ml should become king