@MangaMonger They both relate to each other because they have inferiority complexes toward their older siblings, though Walter's is more in his head.
Walter is attracted to Daleth because he saw her crying about being abused by her sister, sympathized with her and wants to help her. She's attracted to Walter because he understands her, encourages her, and isn't afraid of her like most of the others.
The whole point of the chapter was that Walter doesn't just care about her looks, that's why he still treats her the same when she changes them.