I just noticed that retrieving Relics adds to your Tattoo or as called in the game "tatau", along with skills making your "tatau" more elaborate. I've always had a fascination with tattoos (having many tattoos myself) so it definitely is a part of the game that draws my attention. I have been going out of my way to find things that unlock more of the tattoo. So more specifically, what in game actions unlock parts of your tattoo? For example: collecting relics, completeing sidequests, completing trials of the rakyat, etc.
Another thing I noticed was that relics unlock a different part of your tattoo then skills. Extra credit if you know what unlocks each part.
Update #1
I've also realized that the main quest line also adds to the entirety of the "tatau".
Here is a picture of what I believe makes up the tattoo.
I'm pretty sure all the parts circled with red are skills, the green is definitely from relics and I'm thinking the dots on the other side are as well. The yellow is from relics as well but I'm really iffy on what parts are from relics. The blue is what i believe to be from the main quest line. There is a lot of filler left, so I'm sure there is more that adds to it. I'll just have to keep updating as I go through the game.
Update #2
So after collecting around 60 relics I noticed that there are 4 different types of relics: Heron, Shark, Spider and Boar (no idea why it took me so long to notice the differences since it tells you.)
I believe that as you collect a set number of the 4 different types of relics it adds to that part of your "Tatau." For example say for the first Heron Relic you find it adds a small Heron to your "Tatau", and same goes for each type. Then say you get 10 of a Heron Relic it adds even more Heron filler, and so on and so forth (pretty cool aye?).
Something else I've noticed in the amazing adventures of this game.
Spider Relics:
Require you to do some sort of climbing through sometimes extensive caverns, or across deep ravines. Accomplishing some feat requiring the abilities of a Spider, to get to my point.
Heron Relics:
Tend to be on top high mountains or hilltop, I've even had to use a hang glider to fly onto a clifftop to aqcuire one. Requiring the abilities of a Heron, see the trend yet?
Shark Relics:
Can be found usually underwater, or in a cavern underwater. Requiring Shark like abilities.
Boar Relics:
Requires you to break through a wall, I usually just use a grenade to accomplish this.
Pretty cool I think. I've found it to be incredibly fun to search for Relics, as almost every Relic is hidden differently.
Best Answer
From what I can gather, the relics only put points towards the dots and when you complete the story and the relics and purchase every skill, then it completes it. As you progress through the story, it unlocks the wave like thing at the bottom above the larger 2 sharks, spider and heron. Then, later the story unlocks the tree and the vines beside it. and the mask demon in the middle. I beat the game and only thing I have yet to unlock is the 2 wings at the top and all the dots that trail up to it. Which means I need all the relics to get the wings up top.
Edit: The blue you circled is in fact, from the main story. also right above the middle with the 2 faces is a tree, the tree is from another main story quest. All the rest which you labeled in red and yellow are from skill unlocks that you buy with skill points. when you spend points in spider, it goes towards spider art work etc. The relics only give those dots that you circled in green. I believe that when you get all the relics/ collectibles that you get the 2 final "wings" up top, As you can see, each dot represents 1 relic. Everything else is via main story/ spent skill points towards the animal type. basically that means each line of dots that lead up to the top Shark picture on each side equals 60 relics. since there are 120 relics in all and 2 sides. The memory cards may also play part in the tattoo. Maybe part of the line up top above the wings.
edit #2. Relics only unlock the dots and the wings at the VERY top above the heron's. I know this because I -maybe- collected 5 relics before I beat the game and everything was colored in besides the dots and the 2 wings up top. Right now I am sitting at 24 and the dots, which I counted are 24, is right above the head of the seagull looking icon just above the wave that you highlighted in blue. Now, you do of course get XP from the relics and you might've spent points before looking at it again and thought that, but I was too lazy to get the relics and focused mainly on the story. I could probably show you a picture? Since you have more relics than I do you can see the difference.