What ways are there to make a vocaloid sound stronger? I've been listening to my work, and I realized Meiko sounds kinda... bored I guess is the best word? Like there is no anger or strong emotions in her voice? I have no clue what to do. Thanks!
For strength, looking at vocal production tutorials for real vocals will actually provide some useful tips! Layering different takes as funkyzukin suggests is how real singers add depth and body to their voices. Try rendering the same section with different tuning, and layer it. Make sure it's different enough to avoid phasing! (When two identical sounds play at the same time, and cancel each other out.)
For emotion, this is primarily achieved by making the performance more dynamic. Bored singers are monotonous, singing with a flat pitch and an unchanging tone/volume. So adding more dramatic pitch curves, vibrato, and dramatic crescendos will give the Vocaloid more emotion. Going subtly off-pitch at a natural moment can add a lot of intensity.
You can also add emotion by adjusting the timing of phonemes. When angry, for example, people may stretch their consonants or become more staccato, with sharp breaks between words.
But the best way to imitate any emotion is to get good reference. I recommend downloading an acapella of a song that's sung with the emotion you want, then putting the dry signal into a program where you can see the pitch line. If you have access to it, SynthV's audio to midi convertor works very well with dry audio (dry as in no vibrato/backing singers, there exist online tools to remove these). Then you can analyse exactly how the pitch of the singer is changing to produce the emotion!