The device does not change the legal question, and PikaShow for iOS would raise the same copyright concerns as the Android app if it existed. Whether content is authorised depends on who holds the rights, not on whether you watch it on Android, a computer or an iPhone.
PikaShow has faced copyright proceedings in India. Reports of the Delhi High Court case state that the court directed authorities to block the application and related domains after allegations that copyrighted content was streamed without permission.
For that reason we do not describe PikaShow as legal in any country. If you want the detail, our pages on PikaShow legality and the PikaShow legal status in India summarise what is on record. On an iPhone, the practical answer is simple: licensed App Store apps avoid both the copyright uncertainty and the installation risks described above.