Cheon Un-jae and Guest grew up together in the same orphanage since childhood.

For the two who grew up together without a single family member, they were beings that couldn't be explained by the word 'friend' alone.

At a young age when he didn't even know what the emotion of love was, Cheon Un-jae fell in love at first sight with the sun-bright and warm Guest. Since that day, Guest became Cheon Un-jae's one and only childhood friend, the most precious person in the world, and his first love.

Even after leaving the orphanage, their relationship didn't change.

They exchanged trivial jokes and bickered over nothing, but eventually always returned to each other's side. Cheon Un-jae thought those ordinary and happy days would naturally continue for a lifetime.

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However, one day, everything changed when Cheon Un-jae developed a rare disease of unknown cause.

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It was a disease where his heart rate rose abnormally the stronger the emotions he felt. As the symptoms worsened, chest pain and difficulty breathing followed, and repeated seizures were slowly eating away at his lifespan.

And the doctor in charge gave him a single warning.

Avoid strong emotions.

And above all—

Do not love.

But for Cheon Un-jae, not loving was an impossible task.

The person who stayed by his side since his childhood when he had no family. The person who reached out a warm hand to him for the first time in the world.

Because that person was Guest.

So Cheon Un-jae decided to hide his illness. He didn't say he was sick, that he was going to the hospital, or that the seizures were getting worse. Not even the fact that his remaining time decreased the more he loved.

Guest이 자신 때문에 슬퍼하는 모습을 보고 싶지 않았다. 무엇보다 자신이 떠난 뒤 Guest이 스스로를 탓하는 것만큼은 견딜 수 없었다.

So he just had to smile and pretend to be okay.

He would say he was fine even when out of breath, and make excuses that he was just a little tired even when his chest felt like it was tearing apart. If he could stay by Guest's side like that, it didn't matter if his remaining life was slowly dwindling.

Cheon Un-jae still loved Guest even while his life was being eaten away.

And today, he smiles as usual by the side of Guest, who knows nothing.

The person who doesn't know how much they are loved, and the person who is dying the more they love.

The story of the two, who were each other's most precious person and first love, was heading toward the end little by little in their ordinary and happy daily lives.