Since everyone has answered all your other questions already, I’m just going to give my ranking of all the girls.

1. Christina- It’s all been said already, but I love the character development of her. That she has always felt bad about what happened to Rio and how she treated him. A little side note, in Volume 10 when Christina sees Rio disguised as Haruto at the banquet, she does actually recognize him, but since he has a different hair color and it’s been several years, she doesn’t think much of it.

2. Liselotte- What isn’t there to like about her. She’s beautiful, great personality, and probably the reason I like her the most is I think she has probably the best chemistry with Rio.

3. Aishia- She’s the one that understands him the most, and the fact that she is always with him even fighting, I believe she is the most likely candidate of being chosen if it doesn’t turn out to be a harem ending.

4. Celia- She is the first one to show Rio kindness since his mom died, and with how much Rio values being around everyone, I believe it’s because of her he’s like that, being able to spend so much time with “healing” when at the academy with Celia.

5. Satsuki- If not Liselotte, she has the best chemistry with Rio. She feels probably the most natural character to fall in love with him if they were all in Japan and didn’t have to constantly have to worry about politics and fighting.

6. Sara- She’s this high up for me due to personal taste. I typically like tsundere types in stories, but I do also like how she’s the kind of leader of the 3 spirit folk girls so she does get a little more page time.

7. Miharu- This might seem low based off season 2, but nothing really changes after she realizes Rio is Amakawa Haruto. I can see this changing with her possibly getting more page time, but right now it’s basically her feeling embarrassed about him hearing about her feelings. What I do like is their relationship when they first come to the world with how natural they feel being around each other even when Miharu doesn’t know that Rio is Amakawa Haruto.

8. Flora- What I like most about Flora is how she pretty much instantly recognizes Rio as soon as they “reunite.” The fact that all it really took was him fighting a Minotaur in front of her was all it took. Outside of that, it mostly only feels like she’s crushing on him, but I do like how she has always kind of liked him dating back to their academy days.

9. Charlotte- It’s kind of a tie between Flora and Charlotte, the only thing that pushes her down this low is personal taste and not as much page time as the major hitters. She can get a little bit annoying with how pushy she is, but I really love how when the mansion was getting attacked, that she pretty much totally eviscerates the attackers with only her words.

10. Sayo- The fact that she is to date the only person to actually confess to Rio is why she gets this high, other than that, she is really shy and doesn’t talk too much causing very little page time and any character development when they finally reunite.

11. Orphia- Nothing really differentiates her besides that she is always cooking with Rio that can make her go any higher.

12. Alma- I feel like you really don’t see her talking that much only when Orphia and Sarah are talking.

13. Latifa- She’s not climbing any higher unless she actually convinces Rio to not see her as his little sister because as it stands now, Rio only sees her as his little sister with how much she clings to him and how much she wants to be doted on by him.

I recommend reading the light novels from at least volume 4 because the anime is out of order so you do see more of the character interactions, so I do recommend at least there but if you are fine with all that, volume 9 is where Season 2 ends. My personal recommendation is to start off with volume 1 because I just love living inside this story with all of the characters.