Mawashi uke is a common technique found in all Nahate based systems (Goju, Uechi, Tou’on). In Tou’on-ryu this technique is found in the traditional kata Sanchin and Bechurin and is referred to as ‘tomoe-uke’ (巴受け). It is an extremely powerful technique that is often applied as a strike. This is a completely valid application of the technique, but expresses only one dimension of it. An alternate name for this technique is tora guchi (虎口) – the mouth of the tiger. The choice of name is quite interesting as it evokes a rather terrifying image of a tiger consuming its prey. But why this name? As you are probably aware there are superficial (omote – 表) and deeper (ura – 裏) applications of techniques in Karatedo, and this includes tora guchi. In this light, the striking application can be seen as an omote application, but a deeper or ura application would be the use of tora guchi in some other manner. I think most people who practice Nahate systems have thought of this and may even have stumbled onto a few alternative uses for tora guchi during their practices. But I would encourage the reader to delve deeper into it. Indeed there are countless Jujutsu-like applications for tora guchi: locks, throws, sweeps, traps, etc.
I suspect that if your background is sports-based Karatedo, then these applications may not be readily apparent, but with a little effort and experimentation outside of a sports Karatedo context, they will reveal themselves to you little by little. Of course it helps if your teacher is knowledgeable of these techniques, but it is not essential – just a training partner and a willingness to experiment. I mentioned that tora guchi has grappling applications to it because of specific teachings that I learned in Tou’on-ryu. In the Tou’on-ryu version, the arms are not extended out to project energy as you would as if trying to strike (this is more apparent in the Uechi-ryu interpretation and less so in the Goju-ryu version but still present), but instead the arms (especially the elbows) are kept close to the body. Also the position of the palms are quite different with the upper hand in front of the collar bone and the lower hand in front of the groin. From this position one can easily “devour” an opponent. In closing I will leave the reader with a kuden (口伝) to contemplate the meaning of this technique, “the tiger always catches its prey.”