Rereading this and man, I still give mad props to Nishioka. He knew what was going on and handled it in the most perfect way possible to avoid embarrassing her at all when as we've seen, many boys that age would have been really immature about it or even just awkward at best. What a bro, I'd fall for him too.
Also like, I get the Japanese don't like talking about sensitive subjects but for fucks sake mom, you can't just throw a pad (or worse, a tampon) at a young girl and say "good luck". In the case of pads it's not rocket science but still, you can at the very least tell her how to stick it on and how often to change it until the school steps in to do your job for you.