Fuga: Melodies of Steel 2

beginning in Chapter 3 you will start to come across Ruins (2D adventures where you avoid traps, solve puzzles and defeat enemies while searching for a key to open a treasure chest)

to obtain an S rank, you need to:

• defeat all monsters
• obtain all items (blue orbs)
• obtain treasure (open the treasure chest)

once you open the treasure chest, the Expedition is over and you will receive a rank (thus do not open the treasure chest until you are confident you have done the first two bullet points above to achieve an S rank)

in theory, you could spam these Expeditions during Intermissions if you wanted to rush this achievement but if you are going for a 100% achievement run you will probably get this naturally unless you actively decline to do the Expeditions you come across in each chapter (achievement unlocks upon the completion of the 10th Ruin in which you attain a rank of S)