One of the ways many of us understand things is by comparing them to other things. If you are trying to get a feel for Shintaido by understanding its relationship to other martial arts, here are some pointers that may help.
Shintaido’s history is most like that of Aikido; both are Japanese martial arts created by men steeped in the Japanese martial traditions who set out to create something new and transformational, for conscious spiritual ends. Also like Aikido, Shintaido is new (created since World War II). While this means that Shintaido necessarily lacks the long lineage of other arts, it also means that many living instructors have studied with Aoki Sensei, Shintaido’s founder.
Some people classify the martial arts into hard or soft, or external vs. internal. (Admittedly, there is some debate about what these terms mean.) There is room for both in Shintaido, but advanced practitioners tend to emphasize the softer, and more internal, end of things. A beginner first learns to block an incoming strike, and then to blend with it, evade it, or anticipate it. The advanced movements are not powered by muscle, but by proper body mechanics, alignment, centering, and grounding, somewhat like the Chinese art Tai Chi Chuan.
The result of this emphasis is that each area of Shintaido (karate, bojutsu, jojutsu, and kenjutsu) reworks those older, independent art to a greater or lesser degree to bring them into line with Shintaido principles, often making movements larger and more open in the process.