Some characters in the game have alternate versions, often time being much rarer and appearing in a different position (for example Sione being in the Gold position and Sione SP being in the White position). These characters can't be used together in the same team.
At the moment, there are two types of alternate version characters: SP characters and MZ characters
SP characters are rare, limited-time versions of other characters with different skills, who occupy different orb positions than their originals. SP characters are obtainable through limited-time infuses, and periodically through Origin Infuse and Contract Crafting (for 50 Origin Stones). They are only available at SSR tier and their character minerals are a bright red.
SP characters are alternate versions of characters, representing singular moments and unique or defining experiences in their lives, and can be separated from the main story by years.
MZ characters, short for 水着, (lit. mizugi, swimwear, in Japanese), are limited-time versions of preexisting characters. Functionally, they are similar to SP characters in that they have different skills and occupy a different position than their originals (and SP versions), but their aesthetics, skills and biographies are all themed on summer activities. Their character mineral is a bright blue and adds a splash-shaped flourish to their emblem.
Three MZ characters are typically obtainable from June through August in special multi-week summer infuses, while a fourth (Naya MZ and Fredrica MZ) is only obtainable through the limited-time Summer Fantasy and Summer Ceremony) events. During winter they can reappear in Origin Infuse, with the free character available in Contract Crafting for (for 50 Origin Stones).