Board Thread:Off Topic/@comment-27144409-20180503154648/@comment-25936766-20180517022456

Sentry 616 wrote: How could she have a younger sister who's relavent? Anyway, I don't recall seeing her in the anime, so I don't know. She does appear in the anime, but for a few seconds. Though she does have a special dedicated to her.

She becomes much more prominent later on, but Season 1 doesn't get to that point in the story.