( Headcanon sent in by @never_nightly )

Viktor Nikiforov has cancer. Specifically Leukemia.

He was diagnosed, and it made him want to teach ice skating to carry on his legend and help accomplish someone else's wishes, but he didn't quite want to give up yet. When he saw Yuuri's video replicating his routine he felt something in his bones. So, without telling anyone about his diagnosis, he ventures his way to Japan and begins his life with Yuuri, slowly falling in love.

To show his love for Yuuri and to fight the disease in his body, he kept up regular exercise with Yuuri. But as shown in the show, he slowly gets out of breath more and more with each day, and his hair begins to thin out, and Yuuri noticed.

"It feels thin, doesn't it?"

He tries his hardest to show his love to Yuuri until the very end of their journey, The Grand Prix Final. Yuuri gets gold, and as he and Viktor sprint to each other, Viktor collapses into his arms coughing up blood, then fainting.

He then awakes in the hospital and his family and friends are there, and Yuuri and Vicchan are right at his side in his final moments and a final kiss.

"I love you Yuuri, we really did it, didn't we? We made history.."