My spoilers are based on the chinese movie.
There is no superpower cross connection.
A bus accident happens and people in the bus get caught up. Bus rammed into a sand truck so we also have 2 drivers. Bus driver is FL's boyfriend and Sand Truck driver is trying to find people and save them in the chinese version.
Saving = person buys a light bulb.
Each couple story focuses on their relationship and how one is trying to save their loved one. E.g. mom is dead and is trying to save her daughter by asking her to purchase the light bulb. Ghost at Author's house is her GF and they fought right before boarding the bus - this GF covered her partner so that she does not die and now switches off all lightbulbs so that GF will go and buy a light bulb. White lady is fiance who has already passed away and is trying to save the guy who got a cut in his abdomen during accident. Old man keeps singing a tune and walking that alley because he is stuck in a memory of dropping his son (korean seems to have changed this a bit with a high school boy)... this guy is coupled with the sand truck man .. who perishes but saves the old man (i assume in korean drama they may do high school boy and that man who is going around looking for people)
FL is alive and is the only person who should not be here, baffling light shop owner. The reason she is here is because she is unable to accept the facts.. and her love and yearning desire to hold onto her boyfriend lands her in this universe