The series's name is called Inuyasha. One of the main character's name is Inuyasha too.The Tetsusaiga isn't really a power, it's a sword that Inuyasha wields. This sword was originally made from the fang of Inuyasha's father. Later on, the sword is broken and is repaired with a fang from Inuyasha to serve as a binding. Inuyasha's father was a demon, so the sword was made that only those with demonic powers, in other words only demons, were able to wield and use the sword to its fullest powers. Inuyasha is a half-demon, his father the demon, and his mother a human. Inuyasha is still able to use the sword even though he is a half-demon. Also, in order to use the Tetsusaiga, you not only have to be a demon, you also have to have the heart of protecting a human. Inuyasha's group is mainly of humans, and he does his best to protect them.
Tetsusaiga : When Tetsusaiga is in its normal form, it appears as an old useless sword with nicks and scratches all over. Whenever wielded by the correct organism (in lack of a better word) it will transform
into this. This is the true form of Tetsusaiga and can be extremely powerful. The two moves of the Tetsusaiga are called the "Wind Scar" and the "Backlash Wave". The "Wind Scar" is basically when the wielder of the sword senses the his own demon power and the opponent's clash and form the perfect place to slice and is able to "kill a hundred in one move". The "Backlash Wave" is on a higher level. The wielder has to take the "Wind Scar" and twist it and force the enemy's own power to reverse and reflect on the enemy himself.