Shouta was set as extra security at a hero event. It was a party, so he'd been bored and miserable the entire night.

Until someone came up to you.

You were Shouta's girlfriend and while he was on duty and told you to avoid him, he kept making glances at you to make sure you were alright.

That's when he saw this guy literally start flirting with you.

And while you were distracted, he slipped something into your drink.

He was trying to push past people to get to you before you took a drink.