I personally think that Hosomi is the prettiest of the Chi-Hatan girls. Are the springy things supposed to be some sort of strength training device to improve her baseball throwing?

HawkeyeNFO said:

Are the springy things supposed to be some sort of strength training device to improve her baseball throwing?

Yes, although the punch line being, it was all pretty much useless work since it has nothing to do with tankery (especially since she's not a loader).

Realistically speaking though, if she had her bare arms exposed to those springs, they would pinch the hell out of them, and would be overall super uncomfortable to wear.

As pointed out by ultraHF300-3 on Discord #translations , the harness used by Hosomi is the same one from the series Kyojin no Hoshi.