Context: in Kimetsu no Yaiba, there are twelve oni 鬼, "demons," called the Juuni Kidzuki 十二鬼月, "Twelve Demon Moons," which are divided into upper and lower ranks, or, more literally, "waxing," jougen 上弦, and "waning," kagen 下弦, ranks..
Daki is the upper sixth, jougen no roku 上弦の陸, literally "the sixth of the waxing [ones] (the upper ones)." The kanji for jougen and roku are literally inscribed in her eyes.
roku 陸, the number "six," is normally spelled 六. The more complicated 陸 is called a daiji 大字, literally "large character," and is used when numbering things formally or more ceremonially.
By the way, in the series the lower first demon Enmu 魘夢 has ichi 一, "one," inscribed in the right eye, and shita-ichi 下壱, "lower one," inscribed in the other eye, as opposed to having kagen inscribed.
