A group of people (including myself) actually spent a bit of time coming up with ideas to a Maui themed legion. SInce people seem so interested, I might as well post it.

Basically...

Maui. Armed with a sharpened jawbone from a greater daemon he slew that had plagued his planet, which is bound to his wrist and can be thrown. Also has a shark toothed chain halberd and a ceremonial combat knife made of an unknown green stone.

Wears artificer armour, every surface etched with carvings displaying the old myths and stories of his home planet, a lot about himself.

Disagreed with the cultural traits of his home planet.

Legion traits.

The legion is equipped with a large number of chain halberds. These are all master crafted and are passed down to another marine on the death of the user, they are inscribed with their history and are treated as highly valuable, more so then the space marines. They treat those green ceremonial knives as badges of office.

During the Horus heresy, they remained loyal, but did not take part in the fighting, instead protecting imperial worlds from the harm.

At around this point, Maui kinda wandered off, some suspect he became a daemon primarch, some think he is searching for some artifact, no one knows, his legion, whom he often disagreed with their culture, which was inherited from his home planet.

Eventually, they split up into chapters, the most notable the Carcharodons. The halberds were taken forcefully by the fledgeling inquisition, and all records of the legion were expunged, from the (erroneous) belief of unnatural sorceries occurring within the legion.

Thats pretty much it...hopes this helps.