In 1996, the astrophysicists were in love.

In 1998, Seohyun died.

Some time before the accident, the lovers had made headway in their research of time travel. Reckless and desperate to have her Seohyun back, Niu Nai tested unfinished theories they'd worked on together. After exploding oranges and turning bananas into mush, she suddenly found the key to transporting objects through time without physically damaging them. She didn't know what effects her trials might have on the human heart or psyche, but she didn't care. She needed to see Seohyun and time was leaning heavily on her shoulders as she worked eighteen hours a day. Sleep was unimportant when there was so much work to be done. Two years had already slipped through her fingers, but her first visit to the past was an incredible high. Eager to find Seohyun, she traveled back to two weeks before the accident. 

She relived the incident several times before realizing she would never be able to save Seohyun. The pain that she'd put on hold to focus on her research, finally came to a head. She needed to do something different. Rewinding time to two weeks before the accident became their meeting space. Niu Nai shared her notes and her discoveries with Seohyun. 

In the past, they worked frantically to fortify Niu Nai's trials. 

To allow Seohyun to work solo as well as travel to Niu Nai's time, they duplicated everything from the present pertaining to the research, into the past. Equipment, text books, even Niu Nai's travel pillow existed in both worlds. They were not true copies, but rather, things Niu Nai was able to purchase twice. She wished she could make a copy of Seohyun and take her to the present -- or future, depending who was looking at it. Sadly, it just couldn't be done.