even though the elements of the worlds are different, the dramas are very similar:

• they’re both fantasy.
• in both, the FL, at first, has a trashy boyfriend who leaves her for another woman.
• in both, the MLs are so precious and care about the FL as if it’s something they can’t control. <3
• they both have beautiful family and friend relationships.
• in both, FL is given a special chance by fate (in DAYS, she makes deal w ML to live cancer-pain-free until her death and one extra wish as long as she wishes for the world’s doom before her death; in SFOT, she travels by deleting old msgs to parallel universe in which she’s still in highschool and can change her failure life as long as she makes sure the ML doesn’t die).
• in both, there’s the concept of “no matter how many times fate pulls us apart, i will find you and love you all over again.”
• in both, the ML will do ANYTHING to save the FL even if he has to sacrifice himself.
• in both, the FL tries to change their ill-fate but fate wins every time.
• they both have side characters’ love story which doesn’t change in this game of fate.
• in both, there is a beautiful twist of fate in the end.

but they’re also different from each other:

• the love story of DAYS is enemies to lovers and is set in modern day while in SFOT it is strangers to friends to lovers (but the ML has always loved the FL) and it happens in 2010.
• DAYS couple are 30-ish yrs old (although ML is immortal, he looks like a 30 yr old) while SFOT couple are in highschool (FL is mentally 30 and travels back in time).
• in DAYS, the ML is not human and a deity exists in whose hands fate lies while in SFOT everyone is human and the rules of universe control fate.