Rewrite the plots, lore and backstories of Ranma 1/2, Sailor Moon, Inuyasha, Baka and Test, IS: Infinite Stratos, JoJo's Bizzare Adventure and High School DxD so that they all take place in the same world in the following order: Inuyasha [Inuyasha manages to get the Shikon Jewel on the first try and uses it to become a pureblooded dog yokai, and the Ashikaga shogunate-ruled feudal Japan effectively ruled by Toyotomi Hideyoshi conquers Korea and takes Sakhalin and the Kurils during the Imjin War of May 23, 1592 – December 16, 1598 against the crypto-Sunni Muslim Han Chinese Imperial House of Zhu-ruled Ming dynasty in the eighteen provinces of Han | Anhui, Fujian, Gansu, Guizhou, Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, Shanxi, Sichuan and Zhejiang along with Guangdong, Guangxi and Yunnan| in the China region and the Ming dynasty's main tributary state, the Han Chinese-Korean Royal House of Jeonji Yi-ruled Joeson Kingdom in Korea, making Korea into a region of Japan along with Sakhalin and the Kurils], JoJo's Bizzare Adventure: Phantom Blood [2007 A.P.P.P movie, but with a more Victorian steampunk mystery, Victorian science fantasy, Victorian gothic horror mystery vybe],   JoJo's Bizzare Adventure: Battle Tendency [David Production anime and canon JoJo's manga arc], Ranma 1/2, JoJo's Bizzare Adventure: Stardust Crusaders [A.P.P.P 2000-2002 OVA, A.P.P.P 1993-1994 OVA], JoJo's Bizzare Adventure: Golden Wind [David Productions anime and canon JoJo's manga arc], Baka and Test, High School DxD, IS: Infinite Stratos. [Baka and Test, High School DxD, Sailor Moon, and IS: Infinite Stratos all take place simultaneously].

Also, Yoshii Akihisa from Baka and Test and Hyoudou Issei from High School DxD are the same person, replacing Orimura Ichika from IS: Infinite Stratos as the first and only known male to pilot an IS unit from IS: Infinite Stratos.

Yoshii Akihisa's older sister, Yoshii Akira from Baka and Test is in fact Orimura Chifuyu from IS: Infinite Stratos in disguise who was adopted by the Hyoudous/Yoshiis in this scenario and just decided to stay with them because she was on the run from the Orimura clan.

Issei also gets a change, his parents are Sirzechs Gremory, now Sirzechs Lucifer from High School DxD and Grayfia Lucifuge from High School DxD in this scenario, making Issei a pureblooded devil and not a human like in canon DxD along with also being the older brother of Sirzechs' and Grayfia's canon son in canon DxD, Millicas Gremory from High School DxD, although he still has the Boosted Gear like in canon DxD.

Unlike in canon DxD, Issei got lost in the human world when he was born and bounced about for a bit before Sirzech and Grayfia found him again, taking him to the Underworld.

However, Issei refuses to accept the fact that he is a devil in this scenario and continues acting as if he is human, which causes Millicas, who is a cute girl in this scenario and the real identity of Himeji Mizuki from Baka and Test, who pretends to be the cross-dressing boy Kinoshita Hideyoshi from Baka and Test to get close to Issei, [Milicas] to have incestuous feeling for him [Issei].

The older Yoshiis from Baka and Test are actually Sirzechs and Grayfia in disguise

The "Baka" in Baka and Test is due to the fact that the non-human students of Fumizuki Academy from Baka and Test, which is the same school as Kuoh Academy from DxD in this scenario, view Issei as a idiot for refusing to accept the fact that he is a devil and acting as a human, albiet a perverted, dumb one.