Well, other than the similar look and hair, consider that Ryuuko is fighting against the top bunch of the city's hierarchy and with her friendship with Mako, one of those who lived among the lowest class. The story might delve into those classification of the citizens and students, eventually resulting in overthrowing(or at least make it more balanced with) the higher ups. In short, Ryuuko is totally Seija. Seems like Trigger staffs have been playing DDC. So this is where she went to after the ending.
