Instead of joining the Council, System Alliance is more like Terminus, independent from Citadel. Casualty for turians during FCW/R314 is much higher than the canon because, during the invasion, Ranma, Herb, and Saffron were at Shanxi.
Shepard is Yukihira. Their grandfather is Yukihira Souma, who's still alive and kicking. Due to Ranma's high Ki, her descendants received some benefits from that, namely longer lifespan, fast healing, and resistance to sickness and plague. The locking of her Jusenkyo curse becomes undone due to the Blessing overpowering the locking's magic. That is also the reason that some of her descendants have the Jusenkyo curse.
Every descendant of Ranma is capable of some sort of martial arts. Some can use their Ki like Ranma, Ki blast, Ki-pocket, and other Ki-based techniques, but most could only use their Ki passively. For those from the Yagami line, they couldn't turn their Ki into another element other than fire.
Their mother, Hannah married into the family, and instead of using Yukihira, their father use Shepard as their family name. Their father, is actually Ryu Kumon's grandson and Jane/John Shepard is his grandchild. His daughter married Souma. Because of that, Ranma allowed Ryu to use Yama-Sen-Ken back, eventually becoming master of Yama-Sen-Ken alongside Ranma as the master of Umi-Sen-Ken. Ryu could use Umi-Sen-Ken, but he couldn't use it to its full potential. Same with Ranma. Can use Yama-Sen-Ken, but not fully. And they rarely use it, as it's clear to them that both Sen-ken is quite overpowered compared to other martial arts styles.
Ranma alone could kick around 2 Reapers if she only used her normal martial arts technique. 10 if she starts using her special technique only. 20 if she only uses Sen-ken style. 40 if she used her weapons only. If all are used simultaneously, she can destroy up to 100 Reapers. Probably.
Btw, the ending I choose for this AU is Synthesis ending, but Ranma and her descendants don't get changed, the same goes for the Musk and Phoenix Tribe. Mostly due to their high Ki.
Notes:
Lol, whenever I played Mass Effect, I always play as a redhead female Shepard and avoided any romantic flag. Why is that? I do however never forget to feed my damn fishes.
I liked reading Mass Effect fanfic with humans evolved without using Eezo or using different technology, but most of them make humanity too overpowered for my taste. I liked it when instead of overpowering humanity, they created a balance between humanity and Citadel. In some parts, Council is being overwhelmed by humanity's advancement, but in other parts, humanity is a complete noob compared to Citadel. "Soon, everyone will hear the screams" by magkiln and Contact by KE12 is a great example of what I'm talking about.