I’d suggest watching or reading the anime or manga series first if you haven’t already, or at least part, just so you get a bit of a feel for the characters.
Anyway, this aired with the movie (Yokozawa Takafumi no Baai) and the version I watched, it was stuck after the credits, so you may have to watch for that. It’s a bunch of little shorts (about 5mins?) of each couple and their Valentines day. And it’s cute (although the whole “I’m a guy so do I buy him chocolates?” thing is a little overused… a lot overused… in most yaoi/shounen ai…). Cute enough for me to ignore the fact the I only really like Kirishima/Yokozawa and YukinaXKisa.
I guess it’s not something you actually have to watch, and it’s not something needed or follows the story line exactly, but I’d still watch it for the cuteness and sweetness.