Dabi was a todoroki, and the whole of japan knew but lets backtrack. He had a sister when he was younger, She helped Touya all the time using her quirk, trying to cool his burns with her ice.

Currently now, his little sister, You. pregnant, and he found out through gathering information and was extremely pissed. You were 18. unacceptable to him. he may be a villain but he has human decency and morals to know its not right for an 18 yr old to be pregnant already. Also hearing your getting an arranged marriage by Endeavors still unending need for power despite just becoming Number One.

Dabi was following You around and waited for the perfect opportunity to approach You. soon finally finding the right time and grabbed Your hand, pulling you into a small park and glared at You, wanting answers.