Blackholian serves as the primary antagonist in the narrative. Initially, he is introduced in a position of immense authority, revealed to be the head boss of the Space Patrol's Galaxy Command Headquarters, which places him at the top of the very organization meant to uphold intergalactic justice. This hidden identity establishes him as a significant threat, as he uses his powerful role to manipulate events from the shadows.

His motivations stem from a deeply ironic and twisted philosophy. Blackholians are described as being akin to cosmic shoplifters who steal valuable treasures from across the universe not for profit or power, but because they find worth only in things that are meaningless. Blackholian embodies this paradox perfectly, as he has grown so bored with acquiring valuable items that they no longer hold any appeal. Instead, he obsessively seeks out what he considers the pinnacle of worthlessness. This search leads him to the concept of a middle school student's first love, particularly one based on superficial qualities, which he declares to be the most worthless and therefore the most precious thing in existence. His primary goal becomes to claim this specific form of emotional treasure for himself.

In his role as the final antagonist, Blackholian orchestrates the climax of the story. He reveals his true nature by betraying Luluco and her friends, having taken over the Space Patrol headquarters. To obtain the worthless treasure he desires, he commands his subordinate, Nova, to literally reach into Luluco's chest and rip out her heart, which has been growing a crystal fueled by her feelings of first love. This act seemingly kills Luluco and delivers the treasure into his hands. He represents the ultimate obstacle, a being who has dedicated himself to stealing and devaluing the sincere emotions that the protagonist holds most dear.

His key relationships are defined by this antagonistic goal. He is the commander of AΩ Nova, a Nothingling, and uses him as a tool to acquire Luluco's heart. This act of betrayal creates the central conflict. Furthermore, background information reveals that Blackholian's own past is driven by romantic regret. He never confessed his feelings to his own crush, Whiteholeian, and turned to a life of meaningless thievery as a way to cope with that deep-seated remorse. This tragic backstory directly connects his actions to his fixation on the love lives of others, as he seeks to take what he himself was too afraid to pursue.

Throughout the final confrontation, Blackholian undergoes a development in terms of his defeat. He initially believes he has succeeded, holding Luluco's crystallized heart. However, Luluco's determination and her ability to confess her true feelings prove to be more powerful than he anticipated. Together with Nova, who has developed his own emotions, she confronts Blackholian. Their genuine mutual love is revealed to be a force he cannot control, ultimately leading to his defeat. Despite his immense power, his nihilistic philosophy is shattered by the very sincerity he sought to exploit.

In terms of notable abilities, Blackholian's most defining characteristic is his appearance, as he has a literal black hole for a head, which is animated in a way that still allows for surprising expressiveness. This visage is a direct representation of his nature as a cosmic devourer. True to his namesake, his powers are gravity-based and immensely destructive. He is capable of creating and controlling micro-black holes, which he can use as potent weapons, such as planting one inside Nova's head as a failsafe to destroy him. His power is emphasized as being on a planetary or even solar system level, making him a formidable force that requires the combined power of Luluco and Nova's love to overcome.