Hi! If it doesn’t go too thoroughly against your style as a writer, you could do a chapter from his perspective. It would allow you to get the reader into his head, and you can let them see the beginnings of how is coming closer to being part of the plot. It’ll also create some interest/intrigue; after all, he’s just suddenly showing up. That will help the reader become more interested in him!
If you have some other side characters, see if you can drop them into the same place and have them casually interacting with each other. This would give you a personality for the reader to grow used to, and you can see that they have an influence on the other characters.