That's because the previous translation guy thought that a "Shaku" was a foot and "Sun" is an inch , which is wrong. Properly, a Shaku is 30.303cm and a Sun is 3.0303 cm, thus 7 Shaku and 9 sun is roughly about 282.5cm which is more or less closer to 3 meters. Corrected now.
According to Wikipedia, the length of the Shaku was standardized in 1891. Before then, the length was different in different places. The article provides an example of 35.5 centimeters, which would result in a sword about 2.8 meters long.
I need to meet the head maid. So will you let me through?If you hand over your sword, we will talk.Pretty stubborn, eh?Interesting... Mh-ha ha ha... interesting!Is this the Scarlet Devil Manor?Who goes there?Wielding a sword, you are a rather suspicious person.That's not possible. Today, I cannot take care of my business without it.Then I will have to send you away by force!Raid
襲撃...and there is next to nothing it cannot slash!Let's play, little girl!!!Forged by gods and men, this black-stained sword spans 7 shaku and 9 sun* in length...
Japanese units, Shaku and Sun. A Shaku is roughly 30.3030303cm and a Sun is roughly 3.0303cm. ※ Perhaps around 3 meters long.