Making a return to Pokemon Ultra Sun is that of the QR Scanning, a feature that can be accessed on the lower screen menu at anytime while playing. This feature allows you to Scan QR Codes of given Pokemon, which will in turn be registered to your Pokedex as being Seen. From there, a player can locate the Pokemon in their given games, that is, of course, if it can be found in such. However, a player can only scan ten given QR Codes at any one time before the Scanner must take time to regenerate.
After catching a Pokemon Species, a player can view that Pokemon's QR Code by going into their Pokedex and viewing that Pokemon's information. Players can then share these codes with friends and others-either in person or online-allowing them to scan the Pokemon QR Code into their Pokedex by using their won 3DS and then being able to search for it on their own. However, Legendary Pokemon, Mythical Pokemon, Ultra Beasts, and other certain Pokemon like Type: Null will not have a QR Code shown in their Pokedex Entry (and thus cannot be shared).
Check Out All The Available Pokedex QR Codes Here!
After scanning each QR Code with your QR Scanner, you will receive 10 Points (sometimes 20 Points for Special QR Codes) for your QR Scanner. After earning 100 Points with your QR Scanner, a player can perform what is called an Island Scan. With this Scan, the Scanner will scan the current Island in Alola you are on and tell you were you can find a rare Pokemon with a special move on that island on that given day of the week. There is one specific Pokemon for every island per day of the week, meaning a total of 28 "Rare" Pokemon can be found by using the Island Scan.
Island Scan Pokemon
Squirtle - Melemele Island - Mondays
Onix - Melemele Island - Tuesdays
Horsea - Melemele Island - Wednesdays
Scatterbug - Melemele Island - Thursdays
Bulbasaur - Melemele Island - Fridays
Litwick - Melemele Island - Saturdays
Charmander - Melemele Island - Sundays
Spheal - Akala Island - Mondays
Combusken - Akala Island - Tuesdays
Honedge - Akala Island - Wednesdays
Beedrill - Akala Island - Thursdays
Grovyle - Akala Island - Fridays
Marshtomp - Akala Island - Saturdays
Ralts - Akala Island - Sundays
Swinub - Ula'ula Island - Mondays
Prinplup - Ula'ula Island - Tuesdays
Grotle - Ula'ula Island - Wednesdays
Pidgeot - Ula'ula Island - Thursdays
Monferno - Ula'ula Island - Fridays
Axew - Ula'ula Island - Saturdays
Rhyhorn - Ula'ula Island - Sundays
Aggron - Poni Island - Mondays
Rotom - Poni Island - Tuesdays
Leavanny - Poni Island - Wednesdays
Chesnaught - Poni Island - Thursdays
Greninja - Poni Island - Fridays
Delphox - Poni Island - Saturdays
Eelektross - Poni Island - Sundays