If you say the Bracha on Sushi is Borei Minei Mezonos...why is the Bracha Achrona we recite Borei Nefashos and not Ahl Hamichya? Thank you in advance.

Shalom, Your question is a good one, as you are correct in thinking that foods with a first blessing of mezonot usually have an after blessing of al ha'michyah. However rice is the exception. Because rice satiates it was given the blessing of mezonot - from the word "zan" to feed or satiate. But as it is not one of the five grains (wheat, barley, rye, oats and spelt) the after blessing is the shorter "boray nefashot". This is true not only of the sushi you asked about, but of all rice. Blessings, D. Sperling