@comrade: Mihawk's eyes are rare. The only characters that have the double circles are:
- Mihawk
- Imu
- Caribou
- Cavendish as Hakuba
Of those four, only the first three have the double circle irises by default.
And only Mihawk and Imu share the same pigmentation (red).
And Imu's eyes were focused on/highlighted in this chapter when she nuked the island in the same way Mihawk's eyes were when Luffy saw a vision of him cutting his arms.
Further indicating that Mihawk's eyes are special is that Seraphim Mihawk preserves those unique eyes, while Boa's Seraphim clones have different eyes.
It is not strong evidence that Mihawk and Imu are related, but to say that the eyes are not rare is just factually wrong.