"Beyond the Boundary -I'LL BE HERE- Future" is a sequel film to the 2013 anime series "Beyond the Boundary," continuing the story of Mirai Kuriyama and Akihito Kanbara in a world where humans coexist with supernatural beings known as youmu. The narrative picks up after the events of the original series, focusing on the aftermath of the battle against the Hollow Shadow, a powerful youmu that threatened the balance between the human and spirit worlds. Mirai, a Spirit World Warrior with the ability to manipulate her own blood as a weapon, and Akihito, a half-human, half-youmu hybrid with regenerative abilities, navigate their evolving relationship while confronting new challenges.

The film explores the emotional and psychological toll of Mirai's sacrifice during the final battle of the series, as she had seemingly disappeared after sealing the Hollow Shadow. Akihito, deeply affected by her absence, struggles to move forward while clinging to the hope of her return. Meanwhile, Mirai finds herself in an alternate reality, unaware of her true identity and the events that led to her current state. The story delves into themes of memory, identity, and the bonds that connect individuals across different realities.

As the plot unfolds, Akihito and his friends, including the witty and resourceful Hiroomi Nase and the stoic Mitsuki Nase, work to uncover the truth behind Mirai's disappearance and the mysterious phenomena occurring in their world. Their investigation leads them to confront a new threat: a powerful youmu that threatens to disrupt the fragile peace between humans and spirits. The film balances action-packed sequences with introspective moments, highlighting the characters' growth and their determination to protect each other and their world.

The climax of the film revolves around Akihito's unwavering resolve to bring Mirai back, even if it means risking his own life. Through a combination of courage, teamwork, and the strength of their bond, the characters confront the forces threatening their reality. The resolution ties together the emotional and narrative threads of the series, offering a satisfying conclusion to the story while leaving room for reflection on the themes of sacrifice, love, and the enduring power of human connection.