This is a bolt in catch can, or "overflow can" for the 8.8 differential swaps. With the ultra low profile cover these diff tends to whip up the fluid and it wants to push out the breather.
To protect your diff from losing fluid over time I recommend these cans which will collect any spit out fluid and then allow the fluid to drain back into the diff after driving. This allows for no loss of fluid capacity.
These are currently available for the Mkiv Supra and IS300 chassis. They come with line and are a bolt in affair. Pics of the IS300 installed can and the Supra installed can shown.