It's a JEDI BRAID!
This is a perfect time for me to bring in my theory that Yuna is in fact a JEDI KNIGHT. The evidence is overwhelming.
First, we must go back 2 years to Final Fantasy X. Here we find the Jedi Master Auron. He says that he lived in Spira originally, and travelled to Zanarkand to help Tidus. Rubbish. He is in fact the legendary Jedi AU-RON JINN, sent through time to train Yuna to be the saviour of the future.
His orders were to travel to Spira, kidnap the real Auron, steal his identity and move in on Yuna. But he couldn't do this easily. He needed to use a special drink to stay looking like Auron. That jug he carries on his waist is in fact POLYJUICE POTION. While this kept him looking like Auron, it put him in a sedate state, which is why he is always so calm.
Upon arrival, he learned that he needed the legendary TIDUS to help Yuna on her way. So he used his secret Jedi powers taught to him by his Master WANG SOLO, and seperated mind from body, and attempted to
jack into the matrix travel to the dream Zanarkand.
He failed. He ended up in the world of Kingdom Hearts, and so went on a great adventure involving hookers and strip clubs, but that's another story. Once finished, he tried again to enter Dream Zanarkand. This time he was successful. Unfortunately he had created a feedback loop between Spira and Zanarkand, and somehow Sin had entered Zanarkand with him. Realising his mistake, he took Tidus out of Zanarkand using the extremely hard technique 'Side-along Apparition'.
Once all together in Spira, AU-RON JINN started phase 2 of his plan. He delibarately brought Tidus and Yuna together, for he needed Tidus to save the planet and die for Yuna. He told Tidus his plan in Luca, and
now you can see the real meaning behind this picture. At Djose Temple when Yuna was asleep, he secretly injected her with a serum called V-TIRUS, which would make her Jedi Powers 10x stronger. This is why she was up late. Unfortunately while doing this, a monk thought that he was performing obscene acts, so Auron had to neutralise him with his lightsabre. Yuna's strange behaviour throughout the rest of the game are a side-effect to the serum.
In the airship, before entering Sin, AU-RON JINN is confronted by Yuna about his plans. He decides to tell her everything. On beating Braska's Final Aeon, AU-RON JINN leaves Auron's body, and travels back to Coruscant.
In the gap between X and X-2, Yuna hones her skills as a Jedi Knight, and wears a jedi padawan braid in memory of AU-RON JINN. She ditches summoning and goes for a pair of customised Desert Eagles. She finds a way, using the force, to have infinite ammunition for these weapons.
Shuyin is in fact the evil sith lord DARTH SHOE YIN, sent back through time to kill Yuna, so the future cannot be saved. The Jedi Council send three Knights - Nooj, Baralai and Gippal to protect Yuna and help destroy SHOE YIN. Just before Yuna defeats SHOE YIN for the final time, she says 'I am going to use the power of...love!'. What you didn't know until now is that she was actually going to say '...the power of THE FORCE'. She almost let her plan slip.
Once SHOE YIN was defeated, the worlds became at peace, and Yuna started her own Jedi Temple in Spira to train the new guardians of the future.
True story.