Yuna shows promise Maybe she ends up part of the Nunally circle instead? I thought Mei's school was an all girl's school?
Cyrille is an interesting choice considering her fate. I am of the opinion the fragmentum recovered her 'feelings' while her body was relatively untouched by it depending on how you treat where it ended up.
Lin might provide some interest as someone unwittingly pulled into Nathaniel's faction via how her grandfather used Nathaniel's research to effectively save her.
Now that I am in front of a computer I can lay out what I have in mind for some of these characters in more detail and respond at the same time.
Yuna, I agree she shows promise and could end up in Nunnally's circle instead. But to answer that question, Mei's school is an all girl's school. I wasn't suggesting Lelouch would attend, but could probably meet her through other means, either by Kiana (since they are in the same class). I am weighing other introduction opportunities, but most feel kinda predictable or too cliched, so I might wait for the story to get closer to that point in the story. That is something I want to avoid, anything that could come off as too cliched or predictable, and why I am asking so many questions on the harem and characters as I want to be one hundred percent sure there will be no cracks or potential issues that could be overlooked since I have gotten way too confident with a story in the past, which has left me prone to mistakes. Especially with characters where there is a lot of blanks to fill in if that makes sense.
Yuna could still be a potential harem candidate for Lelouch, if not a possible back up if needed. I am thinking her home life might be slightly difficult growing up with only her mother and being picked on at school making her something of a recuse, anything else for her character I might decide on how her Herrscher transformation goes, and since there are no actual Herrscher personas I might redo her whole transformation scene, and etc.
Cyrille I thought could be a useful backup option, since she would've been brought back as an experiment by Nathaniel, but with her body modified as well too. In the story Lelouch and company would find a abandoned chest near the base of a steep cliff, finding her remains which had been perfectly preserved by the freezing temperatures and later that following night they would start seeing her "ghost" ultimately leading to them to piece together who she was and what happened to her. I am just not sure if it would work since what fragementum creates might be different from what her resurrected self could be, but would no doubt be open to having a fresh start and probably joins Lelouch's group since he had helped release her from the grip of the Fragementum. Still the biggest question I am wondering, and I am curious if anyone has a different opinion, what could Cyrille bring to the harem and her relationship with Lelouch?
Lin, yeah and while Lin's grandfather, had her changed into a MANTIS for the sake of her wellbeing out of care for her, she would no doubt be made and how she was taken from the life of a Valkyrie she wanted to be, and likely more shocking that Dr. Magi's true superior is a Herrscher too which I am sure would be doozy for her. As for her personality, given how Dr. Magi compared Kiana to her, I might use Kiana as a base of building up her personality expect maybe make her more dutiful and less likely to skip out on class. Everything else I would see where the chips would land, but she would probably join Lelouch's circle of friends and allies, regardless if she ends up as a member of Lelouch's harem or not.
I am only vague on such details for future events in the story since what happens between the current chapter and then may be different from what I've envisioned so I am careful not too set too many things in stone, I like to keep things flexible to avoid being tied down.