As for the chipmunk sound, it's not unusual for female j-pop vocalists to operate one or two octaves higher than the unfamiliar western ear would generally consider pleasant.

There's also plenty of music directly derivative of the vocaloid scene that maintains a similar aesthetic with 'organic' vocalists and dispenses with some of the awkwardness of vocaloid-oriented compositions. Example: https://www.youtube.com/watch?v=hjJMIWyl_l4