Hero of Legend
Member
Art by Atsuko Nishida herself.
http://bulbapedia.bulbagarden.net/wiki/Atsuko_Nishida
Proper confirmation comes from Natsume's Hometown Story PR:
Developed by Yasuhiro Wada, the "Father of Harvest Moon," and his studio TOYBOX in Tokyo, Japan, Hometown Story takes players to a new fantastic world filled with color and hope. With music composed by Nobuo Uematsu, famous for his beautiful compositions for the Final Fantasy series, and character designs by Atsuko Nishida, the designer behind Pikachu and numerous other Pokémon, Hometown Story has a powerhouse team with massive creativity between them that creates a unique setting that players will be able to experience for the first time during next month’s show.
Apparently she also did Minccino and Cinccino, I'd imagine Pichu and Raichu, ah fuck it SHE'S likely done all the Pika clones.
There's a decent number of other designers, NOT Sugimori who did the original Pokemon. Like this guy:
Hironobu Yoshida
http://bulbapedia.bulbagarden.net/wiki/Hironobu_Yoshida
Who did Wobbuffet, Dunsparce, Celebi, Deoxys and Magmortar.
Wish we knew more about the other designers, EVERYONE assumes that Sugimori did all of the first 251 Pokemon (like an urban myth?), I certainly did lol. But that's clearly not true!