On a live music radio show, a letter arrives from the 23 years in the past. Through the letter, the first love and friendships of five friends are revealed.
Unfortunately the movie Unforgettable is not yet available on HBO Max.
| Visual Effects | Kim Han-joon | VFX Supervisor |
| Directing | Lee Eun-hee | Director |
| Writing | Lee Eun-hee | Screenplay |
| Writing | Han Chang-Hoon | Screenplay |
| Sound | Kim Sin-yong | Production Sound Mixer |
| Camera | Ji Sung-yong | Key Grip |
| Production | Choi Ki-sup | Producer |
| Editing | Kim Hyung-joo | Editor |
| Production | Jeong Mun-gu | Producer |
| Production | Joo Pil-ho | Producer |
| Production | Bang Mi-Jung | Producer |
| Camera | Lee Joon-gyoo | Director of Photography |
| Sound | Lee Ji-soo | Original Music Composer |
| Costume & Make-Up | Lee Jin-suk | Costume Design |
| Art | Lee Hyun-joo | Production Design |
| Writing | Kim Jin-a | Adaptation |
| Writing | Hong Chang-pyo | Adaptation |
| Lighting | Song Jae-wan | Lighting Director |
| Visual Effects | Park Choul-yong | Special Effects Supervisor |
