Chobits

Angelic Layer
Effectively a sequel, also by CLAMP, a scientist and female competitor from AL are deceased relatives of characters in Chobits.

Durham County
The daughter has a Chobits poster on her wall, and she is seen during the opening wearing an anime mask although it's not of Chobits. Another girl in the neighbourhood has a similar mask.

Tsubasa Chronicle
Also by CLAMP, a Chii-like character is known by Faye.