To Every You I’ve Loved Before

Shiori's Imaginality is her consciousness or spirit that exists independently of her physical body. In the world of the film, Imaginality is a concept where a person's consciousness can manifest as a ghost-like form after certain events, particularly related to Parallel Shifts. The old Koyomi encounters this manifestation at the intersection, which signals that a shift between parallel worlds has occurred.

Earlier in the timeline, young Koyomi encounters young Shiori during his first Parallel Shift, establishing their connection across dimensions.

Kazune's claim of being Koyomi's girlfriend from the 85th parallel world is a prank she plays as payback. Earlier, Koyomi had forced Kazune to speak at the school's opening ceremony instead of him, embarrassing her. The prank is revealed when Koyomi takes her to karaoke to learn about her experiences, and she admits it was retaliation for the opening ceremony incident.

Koyomi experiences his first Parallel Shift immediately after his grandfather's death. While walking his dog Yuno outside, the combination of the emotional trauma from losing his grandfather and being in a specific location appears to trigger the shift. This transports him to a parallel world where he encounters young Shiori and ends up at the Imaginary Science Research Institute where his father works.

The film establishes that emotional states and timing can influence when Parallel Shifts occur, which becomes important later in the story.

An Optional Shift is a forced Parallel Shift to a specific parallel world, unlike a natural Parallel Shift which occurs spontaneously. In this case, someone deliberately targets Kazune with an Optional Shift, causing her to be replaced by a version of herself from the 13th parallel world. This version of Kazune has experienced the death of her son Ryō in that reality, making her arrival emotionally devastating.

The earlier attack at the exhibition foreshadows the dangerous consequences of parallel world interference.

After the Optional Shift targets his original Kazune, a Kazune from the 13th parallel world arrives in Koyomi's reality. In that world, her son Ryō died during the attack at the exhibition, a tragedy that never occurred in Koyomi's original timeline. She eventually returns to her own world after coming to terms with her son's death, but the experience causes identity diffusion, meaning Koyomi's Kazune is no longer numerically the original one.

The attack at the exhibition where Koyomi saves his family hints at the devastating consequences that could unfold in other timelines.

In Koyomi's original world, Ryō is saved when Koyomi rescues both Kazune and Ryō from an attacker during a family visit to an exhibition. However, in the 13th parallel world that the alternate Kazune comes from, Ryō does not survive the attack, his death in that timeline is what makes the grieving Kazune's arrival in Koyomi's world so emotionally devastating.

Old Koyomi and Shiori fail to recognize each other because they are from different parallel worlds living completely different lives. The old Koyomi at the intersection is actually from Hidaka's world (where he didn't marry Kazune), and his Imaginality has merged with Koyomi's consciousness through a Time Shift. Shiori is also living a different life in this reality. Despite having known each other as children in various timelines, the accumulated differences across parallel worlds have erased their familiar connection.

The earlier encounters between young Koyomi and young Shiori during Parallel Shifts established their connection, which makes the non-recognition at the end more poignant.

Koyomi Hidaka is the name of Koyomi in a parallel world where he did not marry Kazune Takigawa. In that world, Old Hidaka initiates an Optional Shift to reach the old Kazune of Koyomi's world, asking her to send her husband to meet Shiori at the intersection. The old Koyomi that appears at the intersection is actually Hidaka's consciousness (with his Imaginality) residing in Koyomi's body after a Time Shift.

IP devices are instruments that measure the distance between parallel worlds, specifically how many Parallel Shifts away a person is from their original world. When Koyomi checks his IP device after meeting Shiori's Imaginality, it shows an error because the shift has disrupted normal measurement. Kazune's IP device initially reads her world as 85 shifts away from Koyomi's. Koyomi and Kazune later work at the Institute to improve the reliability of these IP devices.

In the parallel world Koyomi enters as a child, he makes a different choice after his parents' divorce, he chooses to live with his mother Mayumi instead of his father. This creates a fundamentally different life trajectory: his grandfather remains alive in this world, his dog Yuno has passed away, and his father works at the Imaginary Science Research Institute. This divergence illustrates how small choices in one world can create drastically different realities.

Koyomi and Kazune become an actual couple after both graduate high school and enroll in the same university. Previously, Kazune had rejected Koyomi's confessions multiple times and their relationship was strained by her prank. At university, Kazune asks Koyomi to be her girlfriend, marking the beginning of their romantic relationship that eventually leads to marriage and starting a family.

The ending is bittersweet because while Koyomi returns home grateful to Kazune for making his life happy, he has just experienced an unfulfilled meeting with Shiori, someone from his past who no longer recognizes him. Additionally, his Kazune has undergone identity diffusion due to the Optional Shift, meaning she is not numerically the same person he married. The happiness is real, but it's built on sacrifice, loss, and the poignant reality that connections across parallel worlds can be permanently lost.