Life Link

A Life Link, simply put, is a link between two people in that if one person dies, so will the other, but both deaths have to occur at the exact same time.

With Noel Vermillion becoming the Eye of the Azure, she also became an immortal. Since Yūki Terumi was able to gain a life link with Noel when she accidentally observed him, neither of them can die. Ragna the Bloodedge shares a life link with Nu-13. A life link in top form, according to Terumi, should make the two people stronger as he comments on how Noel was not able to beat Taokaka in her story mode.

According to Kokonoe in Bang's Section of Help Me, Professor Kokonoe!, it appears that both Jin and Hakumen might also have a life link, due to her comment "If you kill the Hero, then the Black Beast's worst enemy will die too".