It is curious that the idea of 'one got away' (as for example one of the otters) is reversed in the story about how Kuukuu got struck by the flipper of a turtle:

... They all sat down and rested, when suddenly they saw that a turtle had reached the shore and had crawled up on the beach. He [Ira] looked at it and said, 'Hey, you! The turtle has come on land!' He said, 'Let's go! Let's go back to the shore.' They all went to pick up the turtle. Ira was the first one to try to lift the turtle - but she didn't move.

Then Raparenga said, 'You do not have the necessary ability. Get out of my way so that I can have a try!' Raparenga stepped up and tried to lift the turtle - but Raparenga could not move her. Now you spoke, Kuukuu: 'You don't have the necessary ability, but I shall move this turtle. Get out of my way!' Kuukuu stepped up, picked up the turtle, using all his strength. After he had lifted the turtle a little bit, he pushed her up farther.

No sooner had he pushed her up and lifted her completely off the ground when she struck Kuukuu with one fin. She struck downward and broke Kuukuu's spine. The turtle got up, went back into the (sea) water, and swam away. All the kinsmen spoke to you (i.e. Kuukuu): 'Even you did not prevail against the turtle!'

They put the injured Kuukuu on a stretcher and carried him inland. They prepared a soft bed for him in the cave and let him rest there. They stayed there, rested, and lamented the severely injured Kuukuu. Kuukuu said, 'Promise me, my friends, that you will not abandon me!' They all replied, 'We could never abandon you!' 

They stayed there twenty-seven days in Oromanga. Everytime Kuukuu asked, 'Where are you, friends?' they immediately replied in one voice, 'Here we are!' They all sat down and thought. They had an idea and Ira spoke, 'Hey, you! Bring the round stones (from the shore) and pile them into six heaps of stones!' One of the youths said to Ira, 'Why do we want heaps of stone?' Ira replied, 'So that we can all ask the stones to do something.' They took (the material) for the stone heaps (pipi horeko) and piled up six heaps of stone at the outer edge of the cave.

Then they all said to the stone heaps, 'Whenever he calls, whenever he calls for us, let your voices rush (to him) instead of the six (of us) (i.e., the six stone heaps are supposed to be substitutes for the youths). They all drew back to profit (from the deception) (? ki honui) and listened. A short while later, Kuukuu called. As soon as he had asked, 'Where are you?' the voices of the stone heaps replied, 'Here we are!' All (the youths) said, 'Hey, you! That was well done!' ...

Instead of one surviving, we have one who does not. It reminds me about how Lévi-Strauss in 'The Raw and the Cooked' shows how this phenomenon is typical of myths. A myth is a structure which is turned and twisted in different ways but still remains the same.

However, I do not believe him when he (as it seems) regards this twisting and turning as some kind of evidence that the myths are arbitrary. Instead, what I believe is the reason for the phenomenon, is the relativity of view-point: For example, having crossed the equator 'up' becomes 'down' etc.

When Kuukuu must die, that - I think - is because he represents the old solar year. When, on the other hand, only one survives, that is because he is the new year (or other period).

We have found a structure in line Aa1 which divides the glyphs into 5 subsets of 18. This may be because in this line the 'back' (tu'a) of the old year - representing the 5 dark nights exceeding 360 - is described.

First (Aa1-1--14) the solar year is mentioned:

Even here tu'a from last year possibly is seen, viz. in Aa1-1--2. Quantifying this hypothetical tu'a we find 2 * 26 = 52 'black nights'.

We can subtract the 6 glyphs of 'living sun' (Aa1-5--10) from the sum 90 glyphs in line a1 to arrive at 84 (= 6 * 14). That could indicate 8 glyphs (Aa1-1--4 + Aa1-11--14) as belonging to the moon. 8 * 14 = 112. We are once again reminded about the Aztec Chalchiuhtlicue calendar:

For 'tu'a' and 'new year' we have 42 + 28 = 70 days. Subtracting 52 'black  nights' (Aa1-1--2) there remains 18 days. At Aa1-18 indeed the light is dawning for real:

We could walk around in this number maze forever without reaching any definite conclusions.

Guidance can only be reached by looking at the glyphs. As far as I can see there is no natural way to divide those 5 subdivisions of 18 glyphs each further, into for example 10 subdivisions with 9 glyphs in each.

Dividing the 90 glyphs into 6 groups with 15 in each starts promising, with Aa1-15 being evidence for (k)oti:

The following glyphs in this series (Aa1-30, Aa1-45, Aa1-60 and Aa1-75), however, do not show enough of the wished for symmetry:

Aa1-27	Aa1-28	Aa1-29	Aa1-30	Aa1-31	Aa1-32	Aa1-33	Aa1-34

Unquestionably the four red-marked glyphs above are interesting, drawing attention to themselves. Aa1-75 is the only twin of Aa1-13 in the whole Tahua text. Aa1-60 is a combination of henua and sun in a curious formation with a threadlike appendix pointing backwards (tu'a?), and only in Ab5-76 do we find another glyph combining henua and sun (though here with a thick henua, a fully grown sun and the pointed flame downwards):

Pointed flame upwards appeared in the 'death period' of the day:

Oriented with the cold and black south pole at the back, 'up' in Aa1-32 and Aa1-60 must be 'south', because the pointed flame is at the top of the glyphs. The pointed flame acts as a pointer in a mariner's compass. A picture from Wikipedia:

The toga glyph (Aa1-33, GD73) and the 5-marked reversed tapa mea (Aa1-34) affirms that we are looking at the 'death' season of the sun (which also follows from the fact that sun has descended since noon).

In Aa1-60 we also can see a similarity with Aa1-24:

       

A new sun is appearing as if evolving from a bud at bottom ('midsummer', north).

With the 5 subdivisions there is a symmetry consisting of 'one escaping' (tere) from 'death', as if saved by going onboard a raft with the whole family.

A vessel on the sea is similar to an island (henua). We should remember:

... The ship of Captain Cook was considered a kind of floating island, i.e. henua:

4 March 1779. The British ships are again at Kaua'i, their last days in the islands, some thirteen months since their initial visit. A number of Hawaiian men come on board and under the direction of their women, who remain alongside in the canoes, the men deposit navel cords of newborn children in cracks of the ships' decks (Beaglehole 1967:1225).⁸⁾ 

⁸⁾ For an analogous behavior observed by the missionary Fison on the Polynesian island of Rotuma, see Frazer (1911, 1:184). Hawaiians are connected to ancestors (auumakua), as well as to living kinsmen and descendants, by several cords emanating from various parts of the body but alike called piko, 'umbilical cord'. In this connection, Mrs. Pukui discusses the incident at Kaua'i: 

I have seen many old people with small containers for the umbilical cords... One grandmother took the cords of her four grandchildren and dropped them into Alenuihaha channel. 'I want my granddaughters to travel across the sea!' she told me. Mrs. Pukui believes that the story of women hiding their babies' pikos in Captain Cook's ship is probably true. 

Cook was first thought to be the god Lono, and his ship his 'floating island'. What woman wouldn't want her baby's piko there? ...

... Considering that henua also means 'uterus' and 'placenta' (henua o te poki),

there may be a similarity between the canoe of the sun and the Ark of Noah. The progeny is transported safely across the deep waters, after which the boat is stranded on a mountain top, letting all the live stock spread across the newborn  'earth' (probably spring / a.m.).

stock  A. trunk, stem ... B. supporting structure; frame of timber for punishment ... C. hollow receptacle ... D. massive portion of an instrument ... E. line of descent ... F. part of hose ... G. fund, store ... H. object of contemptuous treatment ... I. stiff neckcloth ...

The tree trunk is a symbol for the origin of all the rest of the 'tree', a stiff store of life ...

If a long tree trunk is adjoined with shorter ones a raft can be constructed. Possibly the form of GD37 (henua) originates from the form of a raft. I guess the similarity between ocean-going rafts and the small islands in the Pacific may explain much. A ship approaching an island is equivalent with an island approaching a ship.

Another part of the 5-fold symmetry seems to be the 'double' concept. In Aa1-35 it comes clearly forward:

There are two survivors! We can see their heads. Given that they together represent the new coming day, supposedly they are rising sun and sinking sun:

In the first set of 18 glyphs 'double' is also observed:

Not only in Aa1-16 do we find the top flame converted into two (reaching number 7 for the night, instead of the usual 6), but also in Aa1-18 on the rei arm we can see two 'flame' signs just as in GD13:

Even more clearly can we see the 'twins' in for example this picture (from Heyerdahl 3):

I guess that initially the phases of the moon (symbol of life and death) governed the ideas. In one end of the cycle we find waxing moon and in the other waning. Growing and declining.

The points of changeover immediately are recognized: full moon and black moon. I hesitate to use the term 'new moon'. There are two 'persons' and the 'death' of one means the 'life' of the other, his 'twin'. In the picture above the two phases are oriented in opposition.

The 'twin moon persons' are connected and a great solar grin in the middle tells us who is the boss.

In GD13 the message is conveyed in a somewhat different fashion and we remember Fischer's suggestion:

... Throughout Polynesia, the word rei signifies a neck ornament of some kind, perhaps internationally best known as Hawaii's lei ('flower necklace'). Easter Island's rei miro ('wooden rei') are without parallel in Polynesia.

However, they display a form that is strikingly similar to the silver crescent gorget worn by Cook's Marine Officer Gibson who accompanied Cook on all three voyages, including the one to Rapa Nui in 1774. Such silver crescent gorgets was prescribed dress for a Marine Officer of the British Royal Navy in the second half of the eighteenth century. Rapa Nui's rei miro were attested only after 1774 ...

The gorget is silvery and therefore the ship of the moon. The solar grin has disappeared.

The use of GD13 should reflect this. In Saturday, the dark day, moon must be ruling and that explains why GD13 is found in Saturday:

56 (in Hb9-56) equals 8 * 7, where 8 presumably means 'complete', while 7 of course points to the moon.

Continuing this trail of thought one step more: In the beginning of the week, in Sunday, we find GD16 (vai) as no. 18, a sign of (the first phase of) the sun:

Whereas in GD13 the moon ship is seen sideways, GD16 may be a vertical view of the solar ship. The moon ship indicates two phases, while the solar ship indicates four.

Possibly initially the form of GD16 was influenced by the phases of the moon. In Zehren we find:

At left the '... ING rune, used by the Ingveons, the Cimbrians and the Teutons, which clearly shows how the waxing and waning moon sickles are joined ...'

The two fishes in the middle is a visual representation from the Chimu Indians and at right we have a sign for Pisces.

A very similar type of glyph is located at the beginning of the last line on side b of Large Santiago Tablet: