If you have any problems with any content issues. If you are making OC female characters for MC's harem, make it that he meets one of them in New York while going to gyms for challenges similar to kenichi: the mightiest disciple by getting fighting experience. Show the development of there relationship as well. Btw wouldn't it be cool if one of the MC's harem members being the daughter of Yujiro. Long red hair, blue eyes from her mother and a Hot temper like her father's. It makes sense because Yujiro was a massive Chad that slept around so it doesn't surprise me if he has one in canon. Just see the scenes when Baki and Yujiro finds out about this, be such gold. You could after 5 chapter in do a time skip when Baki does his first Underground Tournament and get involved in it making a rilvary between him and the MC. I just hope you make a OC female Hanma for the MC where he has to tame her.