Man, the parent-child relations of this set are sort of a mess. Long story short: The artist uploaded post #7451179, post #7451163 and post #7451173 as a single post on Pixiv, then deleted that post and reposted post #7451179 as its own standalone post, then a day later took the image of post #7451173, revised it into two variations that are larger in dimensions than the original, then posted them as a two-image post (which you see as post #7456366 and post #7456364).