Right now, I just can't resist talking about this. I think Serah Farron has very cute armpits. In my earlier thread about Serah's sexiest outfits, I liked all of her sleeveless outfits, so that I can see her sleek, toned arms, shoulders, and cute armpits. Lightning also shows her armpits a number of times, both in this game and in the previous game, but although her armpits are good-looking too, Serah's armpits are much cuter than Lightning's armpits.

In this video, when she arrives in the Bresha Ruins, pause the video at about 6:55, and you can see Serah with her arm raised in the air, revealing her armpit:

Final Fantasy XIII-2 walkthrough (009-JP) AF005 - Captured for helping? Screw you PSICOM! - YouTube

There are also some pictures of Serah with her hands behind her head, showing her armpits, on Deviantart.

In her Style and Steel outfit in particular, I think it's easier to see if her armpits get sweaty. As she runs and fights in the game, I can imagine her armpits pumping out a lot of sweat... I just hope that she uses a strong deodorant that can keep her body odor at bay, LOL... (she probably does, but even then, she might not stink that bad...)