Takuma Akutsu stands approximately seven feet tall (180 cm), presenting a physically imposing figure with distinctive black hair, narrow piercing eyes, sharp pointed teeth, and a scar on his right cheek. These traits fostered fear in others since childhood, leading to social isolation and the nickname "demon" (Akuma). This ostracization resulted in severe social anxiety and a tendency to avoid human interaction. His deceased mother was his sole emotional anchor; she instilled a near-obsessive dedication to academic studies as his path to gain approval and become a "good person."

Living as an orphan with no mentioned family beyond his mother, this circumstance facilitated his cohabitation with the nine Saotome sisters. Odin, ruler of Asgard, designated him as an Einherjar—a sacred lover tasked with strengthening the Valkyrie sisters through "Val Love" activities, encompassing romantic or intimate acts. Initially resistant due to social fears and a desire to focus solely on studies, he gradually accepted the mission after realizing the world's survival depended on the Valkyries' power, which grew through their emotional bonds with him. This reluctant acceptance marked the start of his development.

Despite his intimidating appearance, Takuma exhibits kindness and a non-confrontational demeanor. He maintains integrity, never exploiting his position for inappropriate contact without the sisters' consent. Early traits included extreme passivity and prioritizing studying over global threats. However, witnessing Natsuki Saotome's battles shifted his perspective, fostering a complex where he feared combat yet could not abandon others in danger. His principle of always saving the girl became central, driving him to protect the Valkyries despite personal terror. He also possesses exceptional memorization abilities which proved tactically valuable.

Relationships with the Saotome sisters formed his primary emotional growth catalyst. Initially awkward and oblivious to love, he struggled to distinguish mission-driven affection from genuine romantic feelings. Key dynamics include: Natsuki, whose initial disinterest evolved into deep mutual affection after he saved her; Mutsumi, attracted to him despite his appearance; and Itsuyo, who initially saw him as a tool but later admired traits reminding her of her father. Shino Saotome shared a forgotten first meeting from his childhood, having bonded in a hospital where his mother was treated. His interactions gradually reduced his social anxiety, though accidental pervert incidents occurred during Val Love missions.

As an Einherjar, he wielded Mistilteinn, one of three Tears of Yggdrasil, granting regenerative abilities—such as surviving bisection by Garm—and later awakened his Holy Sword, "The Book." This artifact enabled healing hands for Valkyrie injuries and evolved to allow a battle form, enhancing his support capabilities from two to three sisters simultaneously. A significant physical setback occurred when Futaba Saotome severed his left hand during her betrayal, requiring an Asgardian prosthetic. These developments exemplified his progression from a passive figure to an active combat supporter.

His development culminated in emotional and relational milestones. He overcame initial refusal through bonds with the sisters, notably confessing love to all nine during a Val Love session—a sentiment that flustered them. His love epiphany clarified Natsuki as his primary choice, leading to a marriage proposal and their eventual child. This arc transformed him from a reclusive student into a committed protector and partner, fulfilling his mother's wish for him to become someone worthy through actions that saved both the Valkyries and the world.