According to this source:

Fans suspicions about AKB48’s 12.5 generation member Eguchi Aimi being a “CG idol” have been confirmed!

The features of Eguchi’s face were taken from the members, which consists of Oshima Yuko (hair/body), Takahashi Minami (outline), Maeda Atsuko (eyes), Watanabe Mayu (eyebrows), Itano Tomomi (nose), and Shinoda Mariko (mouth). Twelfth generation AKB48 member Sasaki Yukari is confirmed to be the source of her voice as well
Additionally, fans correctly guessed the source of her profile information, which was posted on Glico’s website as part of the promotion. Most of the information was based on the company, such as her birthday (which is the same day that Glico was founded in 1922) and her hometown of Osaka (where Glico’s headquarters are based).

Since the truth about Eguchi Aimi has finally come out, Glico has one more surprise up their sleeve for AKB48 fans. By going onto the official “Ice no Mi” website, fans can create their “own AKB48 member” by choosing parts from any of the forty-seven girls available.