I've never really been into the whole "waifu" thing.
It's frequently just a way of saying "this character is hot" or "I like this character" but, y'know, in a bit of a weirder format?
Well, anyhow, if I had to choose the one waifu I've had:
rule34.xxx/index.php?page=post&s=view&id=4928267S&W to this day is the greatest romance anime I've seen.
Probably not that impactful, considering how it's not my genre in general.