I'm a Spider fan since Day 1 first (especially during the Infiltration era) and an Imperial fan second. Therefore, I'm hyped about the last fiction and its potential implications. I'm probably overeading this, but I see a million way this could end up with an heavily-corrupted Imperial faction... Something I wouldn't mind at all. Keep in mind that Shahai is not a name you drop without reason. In the old storyline, she is one of the foundation of the Spider Clan, a Dark Fortune and the mother of Kanpeki, the Champion of Jigoku that literally destroyed Rokugan...
Possibility 1: Meisheido is corrupted one way or another. Given enough time, it's practionners are corrupted as well and you have the Seppun Hidden Guard with now a Hidden Agenda (manipulated by whatever is corrupting them, Jigoku or soemthing else entirely)
Possibility 2: Hubris. Now wielding a new a powerful magic, the Hidden Guard studies it beyond what is considered reasonable, unlocking a dark and hidden power inside it, eating the Imperial families from the inside slowly, corrupting their purpose
Possibilty 3 (and my favorite): Lovers. As an esteemed guest to the Imperial Palace, Shahai will have direct contact with an impressive number of Imperial officials and dignitaries, including the Imperial heirs. We know the Emperor has more than one child, one of which could be the man who became Daigotsu and Shahai's husband in the old timeline. They meet, they fall in love. The marriage of an Imperial heir is serious business, however, and love has nothing to do with it. Daigotsu (or whatever his name will be) gets promised to someone else (A phoenix would be even better, but this could be a nice ''doomed'' story prize) and both Daigotsu and Shahai are unwilling to be separated. (Love makes you do stupid things) They dabble into forbidden magic to change the Emperor's decision and succeeds. Shahai marries Daigotsu and everyone lives happily ever after.
Or not. First, changing the marriage of the Imperial Heir is a slap in the face for the Clan which was supposed to marry Daigotsu in the first place. Second, by dabbling into maho (or something similar), they opened their soul to corruption and are slowly willing to do more and more heinous acts in the name of the love or what they think is for the greater good of the empire, corrupting others around them while doing so. Given enough time, you have a faction within the Imperial Families, led by the son of the Emperor willing to do anything to make his life better. Maybe he now thinks he is better than his brother to rule the Empire and wants to overthrow him. Or maybe the EMpire is threatened by a neighbour and only he is willing to do the horrible, dishonorable thing able to save ROkugan, but damning everyone. The possibilities are endless and not necessarly exclusive.
Edited by Tetsuhiko