Detective Conan: Strategy Above the Depths

Minako Akiyoshi was revealed as the mastermind behind all three killings on the Saint Aphrodite. She murdered the CEO and her own father (the President) to avenge her real father, who was the captain that died during the Yashiromaru sinking 15 years ago. That sinking was a deliberate insurance fraud scheme orchestrated by the Yashiro Group, and her father was left to die after being drugged. Akiyoshi orchestrated the current murders to expose and destroy those responsible for her father's death.

Earlier in the film, Richard's initial deduction that Akiyoshi was the murderer was actually correct, though his reasoning was wrong.

The Yashiromaru sinking 15 years ago was not an accident but a deliberate insurance fraud scheme orchestrated by the Yashiro Group to collect money while hiding their culpability. The current murders on the Saint Aphrodite were revenge killings by Minako Akiyoshi, whose father was the captain who died during that original sinking. Akiyoshi killed the current CEO and President to avenge her father's death, using the new cruise ship as the setting to confront those responsible.

The Saint Aphrodite was built by the Yashiro Group as a mirror to the lost Yashiromaru, creating symbolic closure for the conspiracy.

Kusaka, a scriptwriter who worked with Akiyoshi on a ship-related project, was manipulated by Minako Akiyoshi into believing he committed the murders. Akiyoshi orchestrated the crimes and planted evidence to make Kusaka appear guilty. She used Kusaka's own troubled past, his father was murdered when he discovered the captain had been drugged during the original sinking, to turn him into a suspect. Kusaka then set off bombs and fled, thinking he was the killer, which further obscured Akiyoshi's true role.

Kusaka's revelation about his father's murder and the 15-year-old conspiracy came during his confrontation with Conan.

Minako Akiyoshi's father was the captain of the Yashiromaru, the cruise ship that sank 15 years ago. During the deliberate sinking orchestrated for insurance fraud, her father was drugged and left to die along with other crew members. This personal tragedy motivated Akiyoshi to seek revenge against the current Yashiro Group leadership who ordered or benefited from that original crime. She later became the ship's sub-designer to orchestrate her revenge plan.

Akiyoshi's position as sub-designer on the new Saint Aphrodite allowed her to plan and execute her scheme.

In the post-credits scene, Conan explained that he deduced Rachel's location by interpreting a small clue: when he kicked a volleyball, Rachel heard a soccer ball, indicating she was in a space bordered by a hard wall that produced a different sound. This sound interpretation led Conan and Richard to locate Rachel hidden beneath the deck, where they rescued her with a fire axe as the ship swayed dangerously.

During the hide-and-seek game, the Detective Boys had created a gold medal from seashells for Rachel, which she was holding when found.

Richard initially defended Akiyoshi because she bore a striking resemblance to his late wife. This personal connection led him to publicly deduce that she was the murderer at the welcome party, though he was actually hoping to prove her innocence due to this resemblance. However, as the investigation deepened, Richard's rational instincts forced him to confront the truth and correctly deduce Akiyoshi's guilt, leading to her arrest.

Richard's personal motive was hinted at early, making his later reversal more significant.

After being manipulated by Akiyoshi into believing he committed the murders, Kusaka panicked and set off bombs aboard the Saint Aphrodite. He then escaped by sea, pursued by the Detective Boys. Kusaka's desperate action was driven by his belief that he was responsible for the killings and his need to flee. His actions triggered a mass evacuation as more bombs threatened everyone on board.

Kusaka revealed his father's murder and the 15-year-old conspiracy moments before setting the bombs.

During the evacuation chaos, Rachel returned to a hiding place in an enclosed area within the ship. As the Saint Aphrodite swayed dangerously from the bomb threats and emergency maneuvers, Rachel was trapped in this confined space and fainted. She remained unconscious until Conan and Richard located her beneath the deck using the sound clue and rescued her with a fire axe.

The Detective Boys' hide-and-seek game earlier set up the context for Rachel's chosen hiding spot.

Conan challenged Richard's initial deduction because while Richard correctly identified Akiyoshi as the murderer, his reasoning was wrong. Richard accused Akiyoshi based on circumstantial evidence and his personal feelings about her resemblance to his late wife, not because of the actual logical chain of clues. Conan recognized that the culprit's motives and connections were far more complex than Richard's simple deduction implied, foreshadowing the deeper conspiracy involving the 15-year-old sinking.

This disagreement at the welcome party set up the central mystery of who truly orchestrated the crimes.

During the evacuation, the Detective Boys created a gold medal from seashells for Rachel as part of their hide-and-seek game. Rachel kept this medal with her even while hiding in the enclosed space where she later fainted. In the post-credits scene, the Detective Kids presented Rachel with an improved, more enduring gold medal, symbolizing their bond and celebrating their survival together. The medal served as both a clue during the crisis and a symbol of their friendship.

The medal was introduced during the peaceful moments before the crisis escalated.