In no particular order,
Yuuichi- Protagonist, overall good character and sometimes pretty funny lol
Nayuki- Mornings eith her would seem pretty interesting and fun, no one day the same as the other
Shiori- Overall her story was the best of all of them and it had some depth. As for her character, the fact that she tries to enjoy life to the fullest and didn't regret anything.
Sayuri- Caring, funny and her overall personality. Willing to do almost anything for her friend and she was the only one to actually explain what the title of the show meant.
Mai- Though she's kind of quiet and not very open to new people, she does have another side. Care alot about her friends as well and isn't afraid to fight back. She adds a supernatural feel to the show which made it felt somewhat "magical".
Akiko- A very carefree, calm and collect motherly figure. Has a great sense of judgement and her personalilty makes her even more awesome. And she has a funny sense of humour.