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1) Akai (赤?) also means "red" in Japanese

2) Oni (鬼?) are creatures from Japanese folklore, variously translated as demons, devils, ogres or trolls. They are popular characters in Japanese art, literature and theatre.

Depictions of oni vary widely but usually portray them as hideous, gigantic, creatures with sharp claws, wild hair, and two long horns growing from their heads. They are humanoid for the most part, but occasionally, they are shown with unnatural features such as odd numbers of eyes or extra fingers and toes. Their skin may be any number of colors, but red and blue are particularly common.

They are often depicted wearing tiger-skin loincloths and carrying iron clubs, called kanabō (金棒?). This image leads to the expression "oni with an iron club" (鬼に金棒, oni-ni-kanabō?), that is, to be invincible or undefeatable. It can also be used in the sense of "strong beyond strong", or having one's natural quality enhanced or supplemented by the use of some tool.

3) Ii Naomasa (井伊直政?) (March 4, 1561 - March 24, 1602) was a general under the Sengoku period Daimyo, and later Shogun, Tokugawa Ieyasu.[1] His family, like Tokugawa's, had originally been retainers of the once-powerful Imagawa clan, and Naomasa, then a very small child, was personally lucky to escape death in the confusion and general chaos which followed the death of the clan's leader, Imagawa Yoshimoto, in the Battle of Okehazama in 1560.[1] Naomasa joined the ranks of the Tokugawa clan in the mid 1570s, rising swiftly through the ranks to eventually become the master of a sizable holding in Ōmi Province, following the Battle of Sekigahara (1600).[1] His court title was Hyōbu-dayū.

Ii Naomasa is regarded as one of the Four Guardians of the Tokugawa along with Honda Tadakatsu, Sakakibara Yasumasa and Sakai Tadatsugu, under the famous Tokugawa Ieyasu. He initially gained notice at the Battle of Nagakute (1584), commanding around three thousand musketeers with distinction. His finest hour was to come at the Battle of Sekigahara, where his unit outpaced those of other generals such as Fukushima Masanori, drawing the "first blood" of that battle. However, Naomasa was shot and wounded by a stray bullet as the fighting was dying down, a wound from which he would never fully recover. The wound also prevented his personal involvement in quelling the last vestiges of the anti-Tokugawa faction in the coming months.[1]

The units Ii commanded on the battlefield were notable for being outfitted almost completely in blood-red armour for psychological impact, a tactic he adopted from Yamagata Masakage, one of Takeda Shingen's generals.[1] As such, his unit became known as the "Red Devils", a nickname he shared.