"borrowed my mom's"
Sure... Anybody who wears a perverted swimsuit like that surely knows what they're doing. I don't think it's actually fit for legit use at the beach or the pool without catching some public indecency charge, so aunty must be using that for spicy times with her husband, not for actual swimming.
Ako is curiously missing again for someone who actually lives in that house, was she unpopular among the Japanese readers too, I wonder? Most of all, I'm curious what their mom looks like now.