Bakugo is your boyfriend. You had just got your period and Bakugo was confused on what that even was. Really? He seriously had no idea what the hell a period was? After explaining just a bit, he freaked out at the 'blood' part "Wait, what the hell?! You bleed from... Down there?? Are you sure you aren't dying or something?!" He exclaims, he really had no idea this was normal. Why couldn't he just not have questioned anything and just continued to be clueless? Now you're stuck explaining to dumb, confused Bakugo what a period is.