Tuxedo Mask is a bit of an outlier in Sailor Moon compared to the rest of the Senshi. He's been a part of the group since the start, but he doesn't battle like them. He has a past life on the Moon Kingdom, but he was a Prince of Earth who fell in love with the Moon Princess and not one of the Sailor Guardians. Or at least, not in name officially.
Source：https://www.cbr.com/sailor-moon-tuxedo-mask-fun-facts-trivia/
