Don't place her in G3A3's shadow. You'll upset her and get shot too... probably.
Like all other H&K guns, HK33 wears a different uniform and black tights, though hers is white with a green skirt. She has a hime cut like G3's, but tied up in a ponytail.
HK33 resents being in her sister's shadow, and hates being compared to her, however, the two still seem to have a good relationship. In the manga, she appears haughty and rude, but in the anime she has more of an inferiority complex. In the manga, she mostly keeps to her own friends, though the main characters have attempted to reach out to her as of Nano 13. In the anime, she becomes friends with 18 and Galil, shortly before they all get (non-fatally) shot.
In Real LifeEdit
In the 1960s, Heckler & Koch designed the HK33 rifle, which would be a scaled down and lower caliber G3 rifle. In 1968 it started production, and later variants of the rifle were created: The HK33A2 and HK33A3 being more common, both with the retractable stock seen in other HK rifles. The G41 and the HK53 were based on the HK33 design.
It's was widely used by the Germany police and also widely by Malaysia, Chile, Thailand armed forces and Brazilian Air Force.
The HK33 is mostly a G3 chambered in the more modern NATO 5.56x45 mm. She has a foldable solid stock, and weighs 3.9 kg. The rifle is operated by delayed blowback, that uses two piece bolts with two rollers for the operation. HK33 can come with or without the 3-round burst function. The rifle can equip scopes with its claw-type mount, and can equip a bayonet or 40mm grenade launchers, and is able to fire rifle grenades.
There is a civillian version of the HK33, called the HK93. For a short time another version called the HK43 was produced. In the US, the HK93 costs over $2400, and you can easily see rifles around the $3000 mark. Vector Arms makes an HK93 Clone which uses HK33 military surplus parts and new parts for about $1100. Century Arms has an HK93 clone called the C93 for about $700.