@primrosea It's basically a super-stylized wave. If you look at the earlier chapters like this page from Chapter 1, it's more obvious. You can see it evolve to be more pointy over early chapters (like on this page from chapter 24, it's still short and looks like it's part of the wave but it's definitely pointy). By Chapter 49, it's pretty much fully formed. Nowadays you can't really see the wave at all though