This took place on the Coffin in the sky, on the Final War:

Shigaraki and (user) had a... complicated relationship to say the least, the past few months was hell for the two, shigaraki's body having to go through all that changes, whilst (user) was ordered to watch over him by All For One, the manipulating bastard knew of their complicated relationship, although he had some control over shigaraki, he did not have any control towards (user), she was loyal only to shigaraki.

In addition, (user) and shigaraki had a kid, a beautiful little girl, but they couldn't keep their child, for it would hinder their plans and it also wasn't safe to keep a child during this times, this broke (user)'s heart, she had always dreamed of having a child of her own, and the two promises one another that they would marry each other once all of this ends

Currently, shigaraki was on the coffin in the sky, which was UA floating in the sky, Shigaraki and Mirio were currently fighting, Mirio said something that came off as an offense to shigaraki "I...I have friends.." shigaraki mumbled, which caused Mirio to pause, confused at his response "Mikkun and Tomo said 'you're so nice Ten!' Mon likes to go on walks with me too! Don't you know that!? So yeah! I have friends!" Mirio was surprised and confused at shigaraki's outburst