There are no regulations about whether a rikishi's chonmage should curve to the right, left or even go straight down the centre, but almost all rikishi curve theirs to the right. One rikishi bucks the trend - Aonishiki currently curves his to the left, reviving an old tradition of Hawaiian rikishi.
First class tokoyama Tokojin, who prepares Aonishiki's mage, explained that former Sekiwake Takamiyama started doing it because, as he was left-handed, it was easier for him to curve it left if nobody was around to help. Other Hawaiian rikishi, whether right or left-handed, copied him and the tradition was born.
At the Kyushu basho, where Aonishiki made his Juryo debut, Tokojin suggested curving it to the left. Aonishiki was rather shy and only tried it a few times, but recently he has specifically asked Tokojin to curve it left.
Musashigawa-oyakata (former Yokozuna Musashimaru) also used to have his chonmage curved left, but there were times on jungyo when a tokoyama wasn't aware and curved it to the right. "It felt strange, so I got a comb and pulled it to the left. Takamiyama was the first because he was left-handed. Then Konishiki, Akebono, me... I was the last, but all the rikishi from Hawaii curved their chonmage to the left."
Musashigawa was happy to learn that the tradition had been revived. "The rikishi of today don't know so much about the past. Aonishiki is doing it? That's great!"
Rikishi can show off their individuality through the kimono and obi. But it seems even in the chonmage, if you look closely, there are hidden expressions and traditions on display.