Hanasei have a hard keratin helmet on their heads, where horns sprout out of — also called the crown region. The crown develops as early as 1 month into the larval stage, but horns only start sprouting 4 years into their child stage. The growth plateaus around the mid 20s, and horns only grow once.
If a horn breaks mid-growing, there are a few outcomes: Growth can presume as usual, though lagging behind the normal horn, resulting in a "dwarf horn". The horn may also off shoot in different directions, depending on how it was broken. Finally, the rarest outcome is a different style of horn sprouting from the stump — often a result from a gene dominance flicking on/off.
Their horns were used in fights for dominance and to showcase health and fitness. Nowadays, their horns are rarely used outside of fighting tournaments. In fact, most view it as a canvas for personal and artistic expression — carvings, shavings and even cutting them off and replacing with caps or different models (often made with clay, but metals and synthetic keratin are also popular) being common modifications.
a. Unaltered horns of an adult hanasei.
b. Horn carvings. The markings shown depict the dry and full phases of a river in Yomi culture.
c. Horn caps. The symbol adorned is religious, from the Obá religion. It signifies faith and daylight.