>>2322253It is, and Ume later did the same thing with Sae and Hiro's names too. Personally, I don't mind their full names remaining a mystery forever. Knowing them doesn't add anything to their character. I think the reason Ume doesn't tell us is because it would disrupt the image of the "family" they've made at Hidamari Apartments. It would feel like she's needlessly separating them.