Yuurei are the same as ghosts but it's the Japanese word for it, it generally goes further than simply a spirit and more of having a hostile intention, like a grudge... yeah. However, you said they're not hostile, and you do not even fear them.
I have some experience, as I have lived in Japan and other Asiatic countries. There's a lot of different kinds of ghosts springing from very common ideas and situations, and the way locals conclude upon supernatural influence as soon as something feels off. What bigcheese said about Japanese people, and other Asian people being superstitious, is true, but he could've said it in other ways.
I'm Asian myself and can attest that superstition is a major aspect of our people's culture, across many countries.
Which I'm not necessarily proud of.
I do believe what you have seen and experienced. But, since you mentioned you don't live in Japan, if there were no previous Japanese people who died in your house, I don't understand why a ghost would take on such an appearance? I am not saying there are no Japanese people in your country, but you're talking about inside your own house.
You don't need to learn Japanese etiquette to display kindness to these ghosts, especially if these ghosts are not the spirits of actual Japanese people, as I mentioned before.
But I have a question for you...
I know now they are my Guardians, that's why they are around me.
We're Zevists, we have GDs? Why would scary spirits that look like Sadako from the Ring, or The Grudge, be protective guardians over you? They look like them, do they even make those same croaky screams, too? I know you said you don't feel scared and that they're not hostile, but...
I conclude that you're seeing neutral entities on the astral that, for some reason, take on the appearance of the yuurei from scary movies or media that you have consumed in the past, like The Grudge.
By this, you admit that you had at some point been exposed to such cultures, so it would make sense that those appearances of ghosts would be in your subconscious. Have you seen 'normal' ghosts near you, too?
I'm not saying you're insane, but we know that what we see with our psychic vision, can be influenced by the idea of what our subconscious feels that something should look like.