Fuga: Melodies of Steel 2

Looks like the scoring system is the same as the last game. Battle rank is based on 3 factors - turn count, damage received, and technique. Each of these will be individually ranked and those ranks will be roughly averaged together to create the battle rank. Keep turn count and damage as low as possible, and raise technique as much as possible using the following score system (you can press a button on the score screen to show these details, it's F on keyboard, not sure what it is on controller).

• 100 points per normal attack
• 1000 points per skill
• 1000 points per weakness hit
• 2000 points per status debuff inflicted
• 3000 points per link attack

I was able to get a battle S rank with 1 S and 2 As as well as 2 Ss and 1 B. I believe these are the minimum ranks needed, but let me know in the comments if you find another combination lower than these two. I wouldn't worry about doing anything specific on your first playthrough as your level will roughly be scaled with the enemies and you have a lot more to worry about. If you still need this in NG+, again make sure you at least use one skill and hit a weakness even on enemies that you can one shot so that you don't tank the technique score.