I had a quick look and found this on http://www.maori.org - www.maori.org - not sure if its helpful or not - hopefully someone else might be able to provide more info.

Our Ngâpuhi mau râkau style is based on the movements of tîrairaka. The superstition around tîrairaka is based on the Maaui kôrero where as a result of tîrairaka unable to hold its laughter Maaui was crushed at the entrance way to Hine-nui-te-pô Goddess of Death. The following information should provide you with all the relevant kôrero.

Hei konei râ.

Apart from hiwaiwaka, tirairaka and tiwakawaka, there are sixteen other dialectal Maori names for the fantail, many of which denote the restlessness of this little bird.

Tiwakawaka is also the name of a grandson of the demi-god and folk hero Maui (Maui-potiki). He was one of the first maori settlers to arrive in the Bay of Plenty more than 1000 years ago, well before the main migrations. This was the time of the explorer Kupe and his grandson Nukutawhiti. Tiwakawaka was captain of Te Aratauwhaiti canoe and is said to have been one of Kupe’s people who stayed on when Kupe returned to eastern Polynesia.

When Nukutawhiti returned in Kupe’s canoe to New Zealand it was Tiwakawaka who came down to the beach to challenge him, no doubt boldly like the fantail. Kupe had seen the fantail, tiwakawaka, on his exploratory trip and noted that it carried its tail feathers erect and could spread them out like a fan. Its challenging behaviour reminded Kupe that he was entering the domain of Tane, god of the forest, and perhaps reminded him also of the mythical battle between the sea and land birds.

Taiaha weapon in hand, the fantail and its companion the owl, who was armed with a pouwhenua, advanced towards the forces of the sea birds. Fantail got into a towering passion and danced and glared and performed all manner of gesticulations. Indeed it is said that the war dance, the haka, owes something to this dance of the tiwakawaka in mythological times, or at least the single action in it of jumping from side to side while brandishing a weapon.

It is, however, in the stories of Maui that the tiwakawaka plays its most important role in Maori mythology. From its refusal to tell Maui where his ancentress Mahuika kept fire hidden, it got its very appearance. In retaliation Maui took the bird and squeezed it so hard that its eyes nearly popped out, hence their prominence now. This also explains why its tail projects so far behind its body and why it flies so erratically.

Let it now be said that the fantail got its revenge in full on Maui for his rough treatment by not obeying his instructions when it accompanied him on his last and greatest exploit to the realms of Hinenuitepo.

In those far off days Hinenuitepo, goddess of night, goddess of death, lived, as she does today, in the underworld of spirits. As mother of mankind she has decreed from the troublesome earliest days of creation that man should live one cycle of life, then die. Maui wanted to give mankind everlasting life. He sought to kill Hinenuitepo and by doing so abolish death forever.

When Maui asked his father what Hinenuitepo looked like, he replied: “you will see that her body is like that of a human being, but is of gigantic size, with thighs as red as the setting sun. You will see eyes of greenstone, flashing like the opening and shutting of the horizon in summer lightening. You will see teeth as sharp as flaked obsidian and a mouth like that of a barracouta, and hair like a tangled mass of sea kelp”.

Maui chose several bird companions besides the fantail to accompany him on his great quest. Because he had the ability to change into many life forms, he was able to travel with these birds to the underworld as a sparrow hawk.

Maui’s objective was to enter the womb of Hinenuitepo when she was sleeping and by passing through her vital organs to her mouth, to destroy death. He said to his companions, “My command is that when I enter the womb of Hinenuitepo, you must on no account laugh.”

So Maui, having taken on the form of the noke worm, then entered the womb but as he disappeared within, Tatahore, the whitehead, burst out laughing whilst the fantail rushed out and began dancing about with delight. And then was roused Hinenuitepo who closed her legs and strangled Maui and killed him.

We've had a fantails fly into several of the houses we've lived in over the years and nothing bad has ever happened ... I'm sure you'll be fine too. Have you had any other birds fly inside before (we had a swallow visit last weekend!).

If you're worried then go ahead and have the house blessed for your own (and your DH's) peace of mind .

Fantails coming inside to me are total bad luck. Get the house blessed.