A bit of worldbuilding, a bit of adventure and a lot of frustrated de-aged main character, who just wanted some lessons in magic and got a vacation in a crazy world instead. 

Rias Gremory SI

Solium, means throne, seat

Excidium, either comes from core scindo (to destroy, ruin, annihilate) or cado (to fall) 

For more art & media look it up on spacebattles or ao3

Third story BUT can be easily read without, First is Grapeshot (Twilight & Buffy), Second is Weissweise (RWBY Weiss SI)

https://youtube.com/shorts/FBv4WogDidk?is=Wi-o3BuQjUfFcfhl


Rias SI video intro