I've taken a particular liking to the last name Mori recently. There's also Ogawa and this site which has a huge list of surnames to choose from:
Wiki_Japanese Surname List
And if you're looking for first names, I generally just think of names in anime's I liked. For example, Tomoe from RuroKen etc.
I think Sesshomaru disguised as a Hajime sounds wonderful. But then there's also Akira and Kyo and Suoh and a whole bunch of other names you could choose.
I hope that helped. (Also, what I like to do is find historical figures and give him last names related to them. I think it just makes the historical connection more "connected").