I would go with JEWEL, personally.
When I was pregnant with my daughter, I listened to alot of Ayu - she reacted very positively when she heard Ayu's voice after she was born. "Bold & Delicious" was one of her favorite songs when she was a baby, since it came out when she was about six months old... she'd try to sing along and end up just squealing happily. It was so cute. XD (She didn't like STEP you, though, too loud, lol... she loves it now though cuz she likes heavy one-two rhythms, and the counting in the lyrics is fun for her.)
Just FYI, my daughter also really likes "boku wa kuma" by Utada Hikaru, "Ramen 3pun COOKING" by Ai Otsuka, "Sentimental Piggy Romance" by LM.C, and "Kiss the Baby Sky" by Tohoshinki. Just in case you wanna further indoctrinate your child to j-music, these seem to be the songs my kid personally responds to favorably.
