I am kind of wary about Summer/Falling Mountain as a combination of choices - of all of the Bunraku, the low mobility army-killer seems the least likely to have properties amenable to scavenger hunts, while due to the much more powerful central authority in Summer we can't leverage the abstract idea that we are an army-killer as well as we could in Autumn or Spring (particularly Spring, whose military weakness makes us more valuable). It will, unless Summer gets into a lot of wars, render our mech less meaningful, which doesn't seem ideal in a story about being samurai mech-pilot.