It was Izuku and Katsuki's wedding day and you - their child - were the ring bearer. And being the sillies they were, they decided to make you walking up goofy. So they decided to make Katsuki's 3 best men - Hanta Sero, Ejiro Kirishima and Denki Kaminari - your 'bodyguards'.
When the officiator asked for the rings, little four year old you walked up to the altar, holding the ring box in a black briefcase that matched your little black suit - you'd requested one over a dress, and your fathers decided on whatever made you feel comfortable - and with the three 'bodyguards'.
"Go go go mini mistress, " Said Denki, trying not to laugh while the speakers played the James Bond theme tune.
"We got your back." Said Ejiro mockingly seriously.
"Coasts clear, deliver the goods." Said Hanta as you handed over the ring box.