The movie sets the stage long before the events of Hunter x Hunter, unveiling a past where the esteemed chairman of the Hunters Association, Isaac Netero, triumphs over a formidable adversary known as Jed. Fast forward to the present, a group of enigmatic cloaked figures infiltrates a prison, liberating its inmates to enlist them in their sinister scheme.
As the narrative unfolds, we see friends Gon and Killua Zoldyck taking a well-deserved break from their quests alongside Kite. Their visit to Heaven's Arena turns into a moment of camaraderie as they rally behind their ally Zushi during the intense Battle Olympia Tournament, accompanied by Wing and Biscuit. Unfortunately, their plans are derailed when Leorio gets ambushed by the mysterious cloaked assailants.
Prior to the tournament, Gon and Killua stop by to see Netero, who is present at the Arena. However, chaos ensues as the cloaked men seize control of the establishment. One of the intruders, Gaki, takes the place of Zushi's initial challenger and swiftly triumphs over him. They also wreak havoc on the security systems, and Rengoku inflicts a wound upon herself, cursing Netero and rendering him unable to use his Nen. Just as the stakes rise, the mysterious leader appears, knocking Gon and Killua from the tower, but the pair cleverly evade a disastrous fall, making their way to a lower level of the building.
Recognition dawns upon Netero as he identifies the ringleader as Jed, a man who was once his friend and the head of "Shadow," a covert unit of the Hunter Association that Netero had to dismantle after they misused a cursed power known as "On," fueled by pure hatred. Jed aims to force the Hunter Association to release the "Black Report," detailing the injustices faced by the descendants of "Shadow," who were wrongfully persecuted post-destruction of their organization. The trio of survivors—Gaki, Shura, and Rengoku—sought to harness their animosity to resurrect Jed, who had once guided them in the dark arts of On.
The action escalates as Gon and Killua make their ascent up the tower, only to be confronted by Gaki, while Kurapika, who is present to support his employer, Neon Nostrade, engages in battle with Shura. Amidst this chaos, Leorio, having made his way through the sewers, reunites with Hisoka, who also assists Kurapika in this strife. After an intense battle, Gon and Killua emerge victorious against Gaki, but in defeat, Gaki follows through on his deadly covenant, self-destructing. Kurapika manages to subdue Shura with Leorio's aid, but Shura’s dying act curses Kurapika with Jed's blood, sealing his Nen and threatening his life unless he embraces On.
Upon regrouping, Gon and Killua resolve to face Jed on the rooftop, while Leorio tends to Kurapika’s grave condition. In a twist of fate, Gon too is infected by Jed's blood, compelling him to embrace On in order to keep battling. Meanwhile, Killua’s convincing words lead Rengoku to relinquish her hatred, resulting in her demise and breaking Netero's curse in the process. Netero meets Jed, choosing a defensive stance instead of retaliation, waiting for Jed’s intense anger to wane. The climax sees Gon purifying the On within him and Jed through his Nen, allowing Jed to find peace in death.
With Jed and the remaining members of Shadow defeated, balance is restored to Heaven's Arena, paving the way for the long-anticipated beginning of the Battle Olympia Tournament.
