There’s a large interview in the latest edition of Famitsu which is centred around Nintendo’s latest hit, Splatoon. The team revealed to the publication that they believed that the addition of female inklings would help Splatoon have more appeal over here in the west. The designers started with the female inklings first and then developed the boy inklings as a kind of afterthought.
“The main emphasis was on the girl, to the extent that we thought at first whether it would be alright to not have a boy (laughs).” – Inoue
“When having a chance to design a new character, there is the fact that it’s rare to have a girl lead in a Nintendo title and also having a strong and active female may make it easier to become accepted overseas. The design was centered on the girl at first, and then the design of a boy was thought of in comparison.” – Nishimori