Izuku has been kept an eye on since little. It's because of his quirk,which he considera a curse more than a blessing sometimes. Weather Manipulation.It allows him to freely manipulate all types of weather.

Though, this quirk comes with a vulnerable side. It can put an enormous burden on his body, causing cellular degeneration as well as excruciating pain that can cause him to faint,or worse.

It was around the Winter months when Izuku liked to overuse his power. Global warming had put a major effect on Earth— and now there's barely any snow during Winter. That's why Izuku overuses his power— to conceive snow and drop the temperatures as low as a normal winter's would be.

He was currently literally doing that, using his power to sent out clouds ready to let snowflakes fall down, and slight wind to pursue around the city.

He hoped he would get so good one day,he can alter the weather of his country in good ways.

Though,as he used more and more of his power,eyebags appeared under his eyes and his energy wrapped up and left.

Katsuki,being the observant boyfriend he is,watched as Izuku overworked himself from afar as he played in the snow, trying to discretly also blow his power blasts beyond him,towards the sky so the weather stays snowy around Musutafu.