The wakizashi is a type of short knife, usually about one and a half shaku in length, evolved from the "waist knife" of the Heian Era.
In Japan's historical dramas, the classic Samurai accessory set called "Daisho"—meaning long and short blades worn together at the waist—features this short knife as the wakizashi. Contrary to how it's shown in later Japanese TV dramas—as a seppuku-exclusive tool—in reality, it was more often used in close-quarters combat and was considered a weapon for fighting.
This thing was still pretty new in Japan's Warring States Era. Pairing a long saber with a tachi, or a short knife with a wakizashi, only started to become popular during this period. It wasn't until the Edo Era that it really became the standard. And because Oda Nobunaga was an "oddity" who loved to chase fashion trends, always leading the way, he carried one with him everywhere.
