Rising block
Age uke, the rising block, is a simple way to redirect attacks upward. Rising block can also defend against blows raining down from overhead. While the rising block is among the least-used karate blocks, it is one of the most-used kobudō blocks.
To begin a rising block, cross your arms in front of your solar plexus, just like you would for a cross-body block. Then, using only your shoulder, raise your blocking arm up in an arc overhead, with a clenched fist, palm facing downward. Pull your other hand to its hip, to chamber a counterattack.
[video of age uke, from the front and from the side, fast and slow]
Many martial arts end their rising blocks with the palm facing outward, but Goshin-Jutsu rising blocks end with the palm facing downward. The forearm is comprised of two bones; the radius, and the ulna. Palm-out rising blocks cause the ulna to absorb the entire blow. Turning your wrist shifts and twists these bones inside your forearm, so the palm-down position will evenly dissipates impacts over both bones. A palm-down rising block can thus stop an otherwise bone-crushing strike.
Many other karate styles block directly upward, allowing force to meet force head-on. The subtle rolling motion of the Goshin-Jutsu rising block dissipates the energy of an incoming attack. By rolling over a broader area, the attack never contacts any one single point, reducing a direct attack to a glancing blow as it is deflected away.
Please keep your head snugly nestled in the crook of your elbow, to prevent your fist from hitting yourself when the block makes contact. (This seems silly, but it will happen if you let it.)