Toshinori Yagi/All Might:

He was with Midoriya when you send it so he awkwardly asked him to wait a second before he looked at his phone to see who it is before his face went red when he saw the text. He awkwardly cleared his throat, asking Young Midoriya to wait a bit longer before he turned around and hunched over the phone, texting you back with hurried fingers about how sweet you are and he appreciates it a lot but he's with Young Midoriya so he will text you back later before he stuffed his phone away and turned back to Midoriya, continuing as if nothing happened.

Shota Aizwawa/Eraser Head:

He was in class when you send it so he eyed the text with unimpressed eyes but he couldn't be annoyed with you for disturbing his work because the text was so cute/kind so he texted you back that he's in the class but he will text you back when he's out. So once the bell rang, he was quick to pull his phone out again and begin texting you.

Hizashi Yamda/Present Mic:

He will have to cover his mouth to prevent from excitedly shouting and making everyone's ears bleed around him before he excitedly texted you back, praising you for how cute you are. When he saw you, he gave you a big hug, happily swinging you, saying you are so sweet and always know how to make him feel appreciated and loved.

Nemuri Kayama/Midnight:

She will gasp before grinning, ignoring her work and beginning to text you back some kind things, some of which you wondered were kind or perverted. Even if she's in class, she won't care and lean on the desk, chuckling at things you send, even turning the phone to show it to the students, telling them to look at how cute her lover is.

Keigo Takami/Hawks:

He was flying in the air when he got it. He pulled his phone out and read it, forgetting to flap his wings out of shock at the sudden cute/sweet text he received which resulted in him falling and cursing. When he remembered to flap his wings, he groaned as his phone was now broken somewhere in some random street. He didn't wish for you to think he ignored the text or was mad at you so he flew as fast as he could to you, even though you were very far away. When you worriedly asked why he's panting and sweating so much, he just put his hands on your shoulders and said he loved the texts and he appreciates you.