I assume the bloody noses suffered by middle-aged Soo-hyeon (Kim Yoon-seok) are caused by his lung cancer and then exacerbated by those mysteriously acquired time-traveling pills. I'd also guess that his oncologist wouldn't recommend jumping across decades while undergoing any form of medical treatment. But his 20-something counterpart a.k.a. young Dr. Soo-hyeon (Byun Yo-han) doesn't particularly care about what side effects are going to be triggered for his older self by shuttling back and forth through the years. He wants to save his dolphin-training girlfriend (Chae Seo-jin), let his future self be damned. If that might mean sacrificing the daughter (Park Hye-soo) he hasn't met yet, so be it. Most people's allegiances are going to be with the living persons they know...
And life gets complicated when you break a cardinal rule of science fiction. Like "Never talk to the past version of yourself." That's a basic no-no. You know, the butterfly effect and all that! So what will be the ultimate sacrifice for love in Hong Ji-Yeong's Will You Be There? And might it involve a puppy named "Potato"? Or the ever-trustworthy Uncle Tae-ho (Kim Sang-ho)? Or his younger but just-as-reliable iteration (Ahn Se-ha)? I'm also curious whether the guy with the magic pills couldn't have provided a placebo so that all those involved only thought that everything had turned out for the better. After all, as that old guy put it: "Life is what happens when you can't sleep."