Here is the full list of all 13 Dangerous Relationship achievements.
Completed with "Akira" Best Ending.
Completed with "Ryouhei" Best Ending.
Completed with "Taiga" Best Ending.
Completed with "Kei" Best Ending.
Completed with "Kei" Good Ending.
Completed the Prologue.
Completed with "Ryouhei" Good Ending.
Completed with "Taiga" Good Ending.
Completed with "Subaru" Good Ending.
Completed with "Subaru" Best Ending.
Completed with "Akira" Good Ending.
Completed with All Endings.
Completed All Main Scenarios, Sequels, and Date Scenarios.