The character whose doppelganger appears in Nightwing #300 is Yuji Itadori, the main hero of Jujutsu Kaisen, who has a strange connection to the story's main villain, Ryomen Sukuna.

As Tom Taylor’s run nears its end, Nightwing #113 works as a makeshift anthology for its #300 issue milestone. Somewhat feeling like an annual, it features three consecutive stories told by T… ...

The ongoing NIGHTWING series in which Yuji Itadori is seemingly referenced first began in September 2016. The series began publication as a part of the DC Rebirth relaunch initiative.

Jujutsu Kaisen's Yuji Itadori in Nightwing issue #113. Earlier this month, Guinness World Records announced Jujutsu Kaisen as the most in-demand anime in the world.