I don't know whether this is easy to implement or possible at all. Since I posted the feature request to make the rel-graphs lockable and that still hangs in the air I thought it might also be a good idea to make double relations within them impossible so that already good relationship graphs cannot be messed up again simply by the way they are arranged.
What I want to ask is that linear related anime might not be cross-linked again.
Like a family tree there are only relations between a generation and the last generation as well as the next generation (not counting in "marriages" which don't apply to anime).
Usually we have to clean up stuff that should not be possible at all.
For instance if an Anime get's a sequel that has an alternative setting and then another season of that anime is produced, it is not necessary to point out that the second season of that anime still has the alternative setting (since it is simply the contiunation of the sequel which already was in an alternative setting).
Same applies to many ather things - there simply is no way to get a possible double relation working, because they always contradict each other or they are redundant.
Now people tend to tell me "but there are ways to have two arrows to one anime".
That's right! I never said it would not be possible to have two relationship arrows leading to and from an anime. It is just that those two arrows would have to come from two completely independant linear relations, meaning that a whole "family" of anime would be "married" to a completely different "family".
I know that after several generations it usually happens that different families "marry" again within each other but like in real life usually that happens after two generations earliest (meaning you can NOT marry your cousin Rar! No you can't! Down boy! *snicker*).
At the moment, event he most complex anime relationships like those of tenchi muyo don't allow double relations in a linear way so I guess for the time beeing it should be safe to prevent "incest" relationships in the rel graph.
But maybe I now talked a lot and the system doesn't even allow it
Who knows...