Keisaku Asano is a 17-year-old second-year student at Seisho Academy and Daisuke Dojima's close childhood friend. He remains Daisuke's sole genuine friend, comprehending him while others criticize Daisuke's hero complex. A childhood kidnapping incident imprinted Milo’s prophecy—"Accept everything"—into Keisaku, shaping his resigned, fatalistic demeanor.

Within the Shibuya Defense Service, Keisaku stabilizes the team as "The Heart," mediating conflicts between volatile Daisuke and members like Gai Steiner. His cooperative nature maintains cohesion, despite his self-described "no luck" outlook. Initially, the organization AHRV prophesied Keisaku as the pivotal pilot for the String Puppet mecha in the Shibuya Drift event, but Milo’s choice of Daisuke overrode this destiny.

During an SDS assault on the Revisions’ base, Keisaku witnesses his mother’s death. This trauma triggers a psychological break. Distraught, he kills Revisions member Chiharu Isurugi by crushing her head as she attempts time travel, simultaneously executing a suicide attack that ends both their lives.

After physical death, Keisaku’s consciousness drifts untethered in spacetime while his body and piloted String Puppet petrify. Later, antagonist Nicholas fuses with Keisaku’s lingering essence to gain immortality and spacetime control. This fusion backfires: Keisaku’s consciousness resists, thwarting Nicholas’ attempts to erase Daisuke from the timeline. Ultimately, Keisaku drags Nicholas into the temporal flow, sacrificing his existence to return Daisuke to the present.

In the aftermath, Daisuke vows to retrieve Keisaku from the spacetime flow, implying Keisaku’s consciousness persists ambiguously across timelines. Physically, Keisaku has brown hair and brown eyes and wears a purple SDS suit.