Character Relationship Map: Blue

Characters

• Kim Jun (played by Shin Hyun-jun) — protagonist

  Kim is an elite navy diver who treats military service lightly and approaches dangerous dives with conspicuous enthusiasm. He is friends with Lee, but their relationship becomes strained when Lee is p...

• Kang Su-jin (played by Shin Eun-kyung) — supporting

  Kang is a diving instructor and Kim's former girlfriend. When she is posted to the unit, her arrival adds romantic tension between Kim and his friend Lee, as both men compete for her affection. Her ro...

• Lee Tae-hyeon (played by Kim Young-ho) — supporting

  Lee is an elite navy diver and Kim's close friend. Unlike Kim, he is disciplined and takes his duties seriously. His promotion ahead of Kim intensifies the rivalry between them, while both also compet...

Canonical Relationships

Family, romantic, and professional connections based on plot evidence.

• Lee Tae-hyeon → Kang Su-jin (Romantic Rivals) — Lee's feelings for Kang form part of the romantic tension between him and his close friend Kim.

  The character profiles state that both Kim and Lee compete for Kang's affection.

• Kim Jun → Kang Su-jin (Former Romantic Partners) — Their past relationship resurfaces during the rescue operation, when Kang expresses hope of reconnecting with Jun while warning that this is her last mission.

  Kang's character profile identifies her as Kim's former girlfriend. During the mission, she tells Jun that she has reunited with him and asks him to v...

Story Dynamics

Alliances, conflicts, and narrative interactions that evolve throughout the story.

• Kim Jun → Lee Tae-hyeon (Social Lifelong Friends Turned Rivals) — Their enduring friendship is strained by competition, disagreements over responsibility, and tension during the dangerous recovery mission.

  The plot says they grew up inseparable and that Jun joined the SSU because he could not bear to be separated from Lee. Years later, Jun challenges Lee...

Story Analysis

The story follows two lifelong navy divers whose strained friendship is tested by hazardous recovery work and an urgent submarine rescue.

Plot Progression

1. Friends Beneath the Water — Kim Jun and Lee Tae-hyeon grow up inseparable and volunteer for the SSU together. Training brings an injury and a dangerous accident, raising questions about responsibility and the risks imposed on di...
2. A Friendship Under Strain — Years later, Jun and Lee remain in the navy, but their relationship is increasingly tense. Jun challenges Lee, while the navy develops the USM and plans Operation Mink.
3. The Dangerous Recovery Order — After Big Mouse is lost, the team is ordered to retrieve it and its data from 155 meters. The operation proceeds despite weather, survey, and diver-safety concerns, with Jun and Lee's conflict complic...
4. The Submarine Emergency — The Han-Ban-Do floods, loses power, and comes to rest on a reef. Signs of life prompt a rescue effort that also aims to recover the USM and black box.
5. Rescue Without Resolution — Kang speaks with Jun about their reunion and her final mission. Divers secure the rescue vehicle and prepare to extract the survivors, but the transcript ends before their fate is resolved.