In this section, I will focus on Kumi Koda's 1000 Words rather than its English version sang by Sweetbox. I consider the former a more accurate interpretation of Lenne's character, and I will use my own translation at this site in hope of introducing a different side to Lenne's signature song from what's already been told. Enjoy!
Unspoken Words
A number of FFX-2 fansites from the past stated that 1000 Words is Lenne's tribute to her love of a thousand years. But I digress. When you look at 1000 Words' original lyrics in Japanese, it's really a mix of Lenne and Shuyin's thoughts rather than Lenne's feelings alone. For example:
"I showed my cold back to you as your journey began
But I was listening (to your voice) all along
Would you be fighting alone?
Are you not the unfair one"
I believe this part was meant to reflect Shuyin's sentiment when Lenne made up her mind to fight for Zanarkand with her life. Knowing Lenne, she probably smiled like usual when she broke the shocking news to Shuyin. Or maybe she didn't tell him much of her resolve based on the assumption that Lenne wasn't a person of many words.
"A thousand words unspoken then
I shall send them to you faraway as wings
A thousand words unspoken then
May they embrace your wounded back at last"
Lack of communication is a fearsome thing. During both Yuna and co.'s last battle with Shuyin as well as his last moment with Lenne in front of the Vegnagun, Shuyin's fury seemed to easily vanish whenever Lenne was present. One would think that if Lenne made her point clear to Shuyin, that she wanted to protect everyone's happiness even if it'd cost her own life, Shuyin might not have gotten himself into the whole Vegnagun business at all. As a result, Lenne's words in 1000 Words were almost like an apology: she must have felt tremendous guilt for making Shuyin go through so much pain for a millenium.
In a nutshell, 1000 Words might not be a duet but its lyrics were certainly reminiscent of one. It's really one of Final Fantasy's most unique theme songs ever, I would think.