Maybe they are prickly on the outside and soft inside?
yeah they are the tsundere of nature XD maybe that means that the uke is like a cactus or that he likes to hug cactuses (people that hurt him?)
Gorou's underwear has cactus prints and Ogasawara subconsciously remembered it, that's why he bought him a cactus postcard (but he realized this only after he saw Gorou's underwear again). Then Gorou got angry and crumpled the postcard, as if he was gonna throw it away, but he didn't bc he still keeps the crumpled postcard on his desk. he treasures it bc it's a gift from Ogasawara. You prolly know all these but I wrote in case there are ppl who missed it.
haha the tsundere point seems to be the one and thanks anyway dude
is there any hidden meaning to the cactuses or something?