The name is an extension of Hatamoto which in japanese means "banner man" or what we'd commonly refer to as a standard bearer. There's also a second meaning which means "under the banner" in a political sense or association with the Shogunate party. Hatamoto's were usually mid to high ranking lords within the samurai class and the title was considered to be prestegious and a posistion of great honor.
According to Battletech game fiction the name was given to the mech due to a fin like heat sink on the mechs back that reminded engineer of Sashimono or back banners that samurai often wore into battle. It's a fairly small part on the model that doesn't really seem all that impressive and it's not depicted in the art despite the prominence it has in creating the mechs image and name.
Here is a more recent rendition of the Hatamoto-Chi done by David White http://www.mechzone.com/ for the Strider's Strikers fan site http://www.stridersstrikers.com/.
Needless to say I absolutely love this piece. It has a much more streamlined look along with the addition of a katana for close combat to further the samurai image.
Close combat weaponry like the swords are only a minimal advatage in Battletech, but regardless of game mechanics they are quite imposing and I think really enhance the style of certain mechs particuarly those of the Combine. A large portion of the samurai culture centers around the sword as it is the embodiment and expression of a warriors honor. That is what inspired my latest miniature conversion.
As the Hatamoto-Chi now has a pair of much more appropriately sized banners I'll be using using one of them for my seven samurai tie in. When painted it will incorperate the banner/standard that the seven samurai create as their symbol during the film. It's most prominantly shown flying victoriously over the town at the end of the film prior to the shot flowing dramatically to the graveyard of swords.