Infectors are encountered in exploration areas. They are usually ex-students of the Colleges who have been infected by X substances, although some have been reported to have escaped from the facility, such as CODE-23. Students at the three Colleges are trained to counter these X substances and infectors through their various abilities and weapons.
They can be obtained through bonuses from Kindness Draws (Sirius), 60 day Sign-In Rewards (Limit-Break Sirius), Event Points Rewards (Super Sirius), Event Ranking rewards (Ultimate Sirius), Arena Ranking rewards (Ultimate Sirius), exploration in the Common zones, and defeating Event Infectors, such as Popo and Elaine. Certain infectors can also be obtained through Reward packs from fighting the World Boss (Commemoriative-Brans).
Event Exploration Infectors
Twice a month an event is held where the player may encounter Event Infectors through exploring the Event Zone. Four infectors can be obtained during each event, with two introduced over a period of roughly 7 days before the next two are introduced. During this time, there are 2 types of Exploration Infectors; common infectors who appear for 2 hours; and berserk infectors who appear for half an hour. Beserk Infectors usually take the ultimate form of the card, although Leenmel's berserk form is entirely different from its ultimate form, most probably due to the error in the game) .
After defeating an infector, "RAIL CHANGE COMPLETE" will be displayed and the player will obtain rewards (cards) varying in rarity. Only after defeating a common infector you may encounter a berserk infector with much more health and higher power than a common infector. A berserk infector’s amount of health and power will relate to your level and its rewards (3* cards and above) are usually better than those obtained by defeating a common infector (1* - 2* cards and/or the 4*/5* infector card).
Reward cards may include the infector themselves.
It is important to note that the event 'infector' is not always classified as a infector in the card gallery; only certain cards, such as Helene, Popo, Commemorative-Brans and Elaine are actually listed as actual infectors in the Star Era gallery, while most cards that appear as an 'infector' during the period of an event is usually a card belonging to one of the three Colleges. The Sirius card series are also listed as Infectors in-game.
Below is a list of all actual infectors; event 'infectors' such as Angela are not included to avoid confusion.