As a franchise grows sometimes it is necessary to add a second season. To avoid adding duplicate characters, we use an assignments system to link characters to the new title.
There is a process to follow to do this properly.
Let's take High School DxD for example.
High School DxD (Series) High School DxD High School DxD NEW High School DxD BorN High School DxD HERO
The first step would be selecting High School DxD to be make franchise ready. From the Newer Franchise Tool you could search for High School DxD, select it and run the macro. The macro will duplicate the series, set it to type Franchise, append (Series) to the title and import all the characters assigned to High School DxD. You can also do this manually using the Old Franchise Tool and editing the titles. Once you have the ID for High School DxD (Series) you can from the profile page of a title you wish to link to it and enter in that ID where it says Set Parent ID :
Characters can then be imported in bulk using the franchise tools, or manually assigned using the Master Assignments Editor. Which can be accessed from the Show Admin tools and following the - Edit Character Assignments in Franchise - link.