I unintentionally watch this movie in 2021 (after all drama of So-min and its pop-out) and I re-watch it after I finished with a lot of confusion “with some explain”. But for me, I have a different point of view from previous explanations

*SPOILERS*
As the SHAMA and the HWAN mentioned, the way HYE-JOONG said in the beginning (also late end) that she "killed" someone. For me, it was not a "physically kill" but it was about "MENTAL kill". She killed HWAN in her memory and he is completely lost in her mind since 4-year-old.

1st, the time-life I figured out that “Present” is 2014
2nd – they are siblings and I believe the – imagination bed scene was just put there for movie promotion. 01:21:48 - 01:22:13 Bed scene with empty Fish-tank switch into a full tank, then JOONG woke up with empty-tank and asked herself this dream or not. And the fact that she cants not know which is real or not.

From the past
- 21-March 89. 01:34:36 SOO-RYUN began her work, then she had an affair with JOONG‘s Dad while JOONG’s Mom could not stand by herself.
- 28-March 90. 01:13:28 HWAN said it was his birthday and the calendar in 1990. He also mentioned that he’s afraid of being FORGOTTEN than dying.
- in late 1990. 01:35:40 – 01:37:01 , In HWAN’s room, SOO-RYUN asked JOONG to take care of HWAN, without her. Which means she was forced to leave as Soo Ryun’s Mom at 37:14 “your baby was taken away again?”
(+1)The rabbit was clean, then it moved to the scene they thrown the clean rabbit with baby HWAN, I think, buried him alive.
SOO-RYUN tried to kill 4-year JOONG – for revenge, but she can’t when JOONG said HWAN's name in her dream (& she loved JOONG). Then she hung herself, left the Pink- Bundle – which hold by her crazy-mom after her death.

1991. 01:28:41 : JOONG’s Mom asked “Are you STILL missing her?” after he refused to hug due to painting. Then, JOONG’s Mom, & grandma, the old concierge death.
28-March-1991: Her dad suicided on returning from France. (it could be 91 or 92 due to the left-diary of JOONG Dad 14:43 )

Until March 2014 - at 07:28 (also at 01:19:44 ) - Calendar is March/ Horse year – 2014
JOONG woke up and made breakfast for AUNT, she got hurt but she told “FOR SOMEONE I LOVE” as she was told by SOO-RYUN at 01:29:25. (after SOO-RYUN got hurt, JOONG took a knife, the camera move back, there is nothing left there, no SOO-RYUN, no cutting board….its not real)
17:47 While the SHAMA talked about a talisman that kills soul, and she said to AUNT “without your mom knowing” (AUNT’s Mom – JOONG‘s Grandmother) and there was another talisman from the one who stared or witnessed the ill-fated circle – Grandma again, well, she also sat there and heard it too.
JOONG just came to Wonderland and couldn’t realize which real or dream, due to her memory, she only dreams about dying which led to blood, anything else.
After all, she remembered HWAN, who was “mentally killed/ deleted” by her memory.
In the end, and once again “GOT HURT FOR OUR LOVE”, HWAN pushed her and opened the talisman to seal him and his mom, to save her life. Then both baby HWAN and SOO-RYUN smiled just like forgive.

(+2)… However, I still have another theory, that when SOO-RYUN was forced to leave. JOONG took care of HWAN.
As she did before 01:53:40 (HWAN cried and was saved by dad). JOONG feed him candy or something like flowers 01:32:56 - she put something in her mouth , and unlucky, JOONG's Mom ignored and Dad came late.
JOONG did kill HWAN by mistake (I don’t think she used a knife due to the clean rabbit).
Which led to HWAN need her remembered him to resurrect to the next life, if not, have to kill JOONG. So HWAN did the same as I mentioned above.

And in 2015, the HWAN picture was blown out by the wind, which is in the song as “the wind, the spirit’s love…my spirit always with her”. For me, it is just a reminder that even HWAN is dead, he is still with her, and She also remembers about him.
“I will always watch over you because I love you deeply in my heart” (sign-language Dad & JOONG & HWAN knew).