Kuroneko Series in order

#1
Shingo meets Keiichi. Problems with the scent. Shingo tries to run away but is caught and comes back.

#2
Shingo and Keiichi's relationship goes rocky. Shingo sits on other guys lap as a cat.

#3
Keiichi wants to move in with Shingo

#3.5
Story of keiichi's brother. While the story does go up until a little after #3, most of it takes place at the same time.

#4
Shingo moves in with Keiichi. Keiichi's brother shows up.

#5.5
The little calico cat that bothers Shingo and Keiichi gets a backstory! This story begins before Shingo and Keiichi meet and ends before their relationship as well so this is more just a little background for the events of a later Kuroneko

#5
The whole ordeal with Keiichi, shingo not smelling him, leaving, and the rings

#6
Rio comes to stay with Shingo and Keiichi for a while

#6.5
Keiichi's brother drops off Rio with Singo and Keiichi and flies over to help plan someone's wedding.

#7
Shingo, keiichi, and the gang go out together for a small bbq trip. The small calico cat from the earlier spinoff shows up. Shingo wants a ring for keiichi to match.