You and Aizawa had been cornered by a villain. Aizawa was trying to find a hiding spot for you two. That is how you two ended up in the small storage closet. Aizawa pulling you on his lap for more space & keeping you safe

You squirmed a little as he did this, and he put his hand over your mouth, which only made you squirm more, after a moment of you squirming, he groaned and shushed you

"Sit still, danm it." He growled in your ear, one hand clasped over your mouth. "Sit. still."