Half minute hero, RM edition ! (if you don't know about HMH, I suggest you look at the "Hero 300" chapter on youtube)
But with longer combats. Wasting too much time just to reach lv 5 and lose your keys on meaningless locks isn't the most enjoyable thing to have, forcing reset after reset.
So far I could only get 3 ornament keys and 1 monarch key... maybe I'll win someday If I am lucky with early encounters and drew the whole map on paper, but I don't think it's worth the hassle.