Itsuki from I"s doesn't look exactly like Ai, but their personalities are so much alike. Both are mentors to the main male characters and are tom-boyish and open. Good teases, too.
Seto from I"s looks similar to Yota, minus the fact he's a few years older. Seto does wear his hair up, while Yota wears his down. Yet their personalities are both the same — hornballs who are undoubtfully kind hearted.
Iori from I"s looks almost EXACTLY smiliar to Moemi. Even their personalities match! As for Tomoko from DNA2, she looks a little bit like Moemi.
Ami from DNA2 and Nobuko... Can you not see the resemblance? :D Short, wavey hair and deep brown eyes. And to boot, their personalities are very similar.
Takezawa, the teacher from I"s, and Rolex... Both don't play a big part, both are tall, dark, and silent, and they have that long, wavey, dark hair. Mmm.