I don't recall the name, but there's another version of The Last Stand of Susano'o that's right above it on the map which has enough missions to get the achievement as long as you don't have too many of the generals on your team that would have been giving said missions. --- Often, when you try too hard to act superior, the opposite occurs.
Don't use any of the recommended characters (they give you missions) and do one of the last chapter battles. I got it in mine on accident. I just accept all the missions, since they're usually "Kill 300 enemies in 10 minutes" "Kill 600 enemies while maintaining over 30% health" and "Kill 3 Officers in 10 minutes with over 30% health" or some amalgamation of the three. --- You can't kick ass and have both feet on the ground at the same time.