Is a waifu considered a collectible?
“Waifu” means “my favorite anime girl”. You don’t collect them, unless you want a harem.
Some people use the word to mean any loveable anime girls. You still don’t collect them.
Picture: a parody advertisement you can see on anime websites on 1st of April.
Maybe some games, like Kantai Collection and Genshin Impact, allow you to collect waifus into your team, but it’s a rather niche case.
You can collect merchandise of your waifu. Figurines, pictures, dakimakura covers an so on.
Picture: a room of a person who went overboard with collecting.