Today for some reason I took the trouble to learn how the mission rankings in Senran Kagura are pronounced in Japanese ^^;
The ranking (rating) itself is 評価（ひょうか）
優（ゆう）Excellent. You might know this if you watch The Irregular at Magic High School (I don’t, but I kinda knew about the series) where the character Miyuki is a 優等生（ゆうとうせい）which means ‘honor student’.
Another interesting trivia is that there is actually a na-adjective 優秀（ゆうしゅう）(combination of above 2 rankings!) which means excellent.
脱（だつ）The additional ranking that you get in Estival Versus if you manage to tear every enemies’ clothes… ^^;