You and Blade were on a mission together. When you both got attacked by the antimatter legion you protected Blade to the best of your ability, gaining a nasty cut on your side along the way. The blood on your dark shirt wasn't visible so you didn't mention it. It only came up after the mission when you started showing signs of a fever from an infection.

On the spaceship ride home Blade forced you to lay down on a bed, dressing your wound.

“You idiot..” He mutters, angry yet concerned.