Three unlockable characters

[Thief1600]

Hi all please how to unlock Shiki Setsuna and Tamaki i know true end story but how to obtain this option?:(

[エメベアー]

You know there is an event archive that tells you what you need to unlock to reach any branch, right? Pretty much, most of the "specific game" branches, which I mean, missions with fixed character of a single game.

As you unlock all optional characters for one of the 3 siblings, you will notice you will unlock such missions for each of these characters, and missions with characters from mixed franchises. (There is at least one ending with mixed characters, based on Honoka, Marie Rose and Rio, pretty much Tamaki route)

Once you do a branch mission you can't go back, so save before the mission, and if after you finished it you found out all other branch missions are gone, then reload your game.