These are sodegarami and sasumata - they are described in GURPS Martial Arts on p. 224 and given stats on p. 230. I suppose this spring-loaded version might offer a bonus to an initial attack at the cost of a slower re-Ready.
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Another weapon set practically begging to be put into the hands of an ultra-strong demon fighter, apparently a very large one who uses sword-and-board style: from Japan's Kofun period archaeologists have unearthed a
seven-foot iron sword and 1 foot x 2 foot bronze mirror shaped into a shield, buried in a Kofun period (ca 4th century CE) grave. They believe the items, far too heavy for ordinary military use, were apotropaic.
What they didn't find was an inhabitant of the grave, so... maybe someone out there wants his stuff back?