After two entire days of working I managed to come up with something reasonable. The song is by Hatsune Miku and called Chain Girl. The context is about a girl who feels like she has no freedom and someone (presumably God) is just using (letting her live?) her because he/she/it's using her like a doll. She's frustrated and lonely, and wants them to unchain her.
I don't know how but I managed to memorize the lyrics easily. It seems I memorize easier when the lyrics remind me of myself, like You and Beautiful World and now, Chain Girl.
I put two voices together because I couldn't decide which one was better. The first one was rather assertive but kind of too rough and the second one was very passive but flat sometimes. So I tried putting them together and surprisingly, the two voices cancelled out the worst of each other!
Afterwards I deleted the incurable parts (like hoarseness, off-tune, wrong lyrics) and rerecorded. I'm really glad I got the hang of Audacity; it proved extremely useful as I removed as much background noise as possible, mixed seven audio tracks together and deleted out poorly done parts. It was very fun to record twice for everything I tell you.
Sayon.