Boy, Lento-san sure lucked out in regard to whom he saved.
She's willing to give him a chance, and she's smart.
Well, kinda smart; not smart in regards to surviving as an adventurer, or she wouldn't have been in the position he first found her in, but smart in regard to extrapolating once she does have a clue.
Such as thinking of bringing a mirror, and getting him a mask that will subconsciously start the process of people thinking of him as a "safe" undead, once he reveals who he is.
And, once someone, like maybe Lento-san, takes her under wing, she'll catch on to what's really going on in regard to surviving as an adventurer.
Like I said, he really did luck out in regard to whoop his first post-metamorphosis contact was with.
He appears, based upon the reflections of his Guild Advisor, to be the one person in the area with the best chance of being accepted by the locals after being turned into an undead, provided he gets the chance to talk to them and convince them that he's still Lento-san at heart, that while the body may have changed, the person inside is still the same.
Saving the girl will decidedly count in his favour.
Mentoring her, as he used to do while human, will cement that.
Now, as to his clothing that she provided, I have to admit that the robe looked more like a duster to me.
Well, maybe not; I just opened the proper page again in another tab to check.
Pity, I think dusters are cool.
I'll admit to not being familiar with garments that button up that high. Looks like it would be useful in a snow/rain/sand storm.
This is looking to be a good manga to follow.
The author understands all the standard tropes of this type of world, and is using them intelligently.
The MC is someone who has demonstrated character traits prior to his transformative event in a manner that supports his reacting to his situation in the manner that he did; his established background holds together, and doesn't require a suspension of disbelief in regard to what happens after his transformation.
He doesn't appear to be a Mary Sue/Marty Stu author self-insertion character; if he is, that speaks very well of what the author wishes he were like and capable of doing.
The harem tag does indicate that there will be those who are able to look past his outward appearance. Given the background provided, in regard to how he interacts with people, I can actually believe this as being possible.
It'll help if his further monster evolution stages become more "living human" in outer appearance, as that will require less on the part of people overcoming their instinctive reactions to his appearance.