PRELUDE Animes

[Êricō]

Anything by CLAMP, basicly.

Somewhat but that is most likely because of "Tsubasa Reservoir Chronicles" but I think only that and "xxxholic" are directly intertwined.

[mirkosp]

"Tales of Vesperia: The First Strike" is a prequel to the events in the video game, and what a prequel it is.

[Ishbalan]

Kyon's sister in Haruhi Suzumiya grows up to be a character named Kurumi Imari to participate in the occult events at a certain school.

[Knowname]

Franchise' like this aren't uncommon though not all are as laid out as Harlock/ Gundam/ Black Jack et all. I really like when they change the lead role but keep largely the same cast of characters, it really makes things interesting I think.