The first is an example of the fairly common musashi plains motif with grass and a goose in flight.
The goose is at the left and outlines the kozuka ana. The smaller kogai ana is a typical trait of the second generation Tadamasa. The long curved lines on the right are the grass and the irregular figures at 2:00 are the grass seed heads. The scale of the circle at the top of the seppa dai suggests a dew drop, but the moon over the plain does figure in some variations of the musashino motif.
This is a relatively small, thick guard and has the typical fully rounded rim. It has a Sasano hakogaki attributing it to the second generation and rating it kessaku.
Here are some variations on this design by Tadamasa from the literature:
Here’s a composite image for easy comparison.
The last guard is the most different. In the first three the figure at ~7:00 appears to be a blade of grass bending to the left. I’m not sure if the fourth is just a further abstraction of that or if it represents some other idea. Musashino is an enduring tsuba motif, and not only within the Akasaka workers.
Akasaka tsuba are known for relatively abstract designs, and the next example tends to confound most viewers on first look.
The asymmetrical and in this case “free form” hitsuana are again typical as is the shape of the full maru mimi. The seppa dai here is a bit more pointed toward the top. This guard is accompanied by an NBTHK certificate attributing it to the second generation and describing the motif as a mortar and pestle (suribachi and surikogi). The rim of the mortar bowl is the ellipse at the lower right and the base is merged with the rim. The curvilinear motive at the top is probably a cord attached to the pestle.
The mortar and pestle are associated with the preparation of medicine and food. It also figures in the monkey and crab legend Saru Kani Kassen which is a bit convoluted but does not end well for the monkey.
Another example is here, with a different reading of the same motif.
These are the only two examples of this design I can think of, regardless of school. As Dr. Torigoye notes it is a modern idea, one of many created in iron by the Akasaka masters.
Update: Additional information on the third musashino tsuba above has been provided by Eckhard Kremers. The following images are his and are much more revealing than the above. Please see his full text regarding this tsuba in the comments section below.
While the caption of the photo from Sasano-sensei’s study group Tosogu Yuhin Zufu attributes the tsuba to the sandai, his personal attribution as shown above is to the second generation.
Interestingly, the walls of the sukashi show clear chisel marks rather than filing, which Eckard points out in his comment below indicates an early date.
The composition of this example is also different from the first three examples, introducing a rotation of the elements as demonstrated here:
Taken together as Eckhard writes in the comments below, this is likely the earliest example of the group.
Additional Update: I took another look at inside the sukashi of the first tsuba:
There’s a bit more rust on this example, but looking all around under magnification I see no signs of a chiseled finish to the walls. I also don’t see file marks, so unknown if this is scraped or filed to finish.
For completeness, here is a look at the hakogaki for that first tsuba from the top of the post:
Hopefully jumping back to the third and then the first tsuba in the post is not too confusing.
Tsuba Kansho 