You should take a look at more of Kikuo's work because he has tons of dark/weird songs. Some examples:
http://youtu.be/4RRvs_sDkRw (Abortion)
http://youtu.be/8ohG6nlpZWU (This one is tricky, personally I think it's about the circle of life and possibly reincarnation)
http://youtu.be/HinT8DXYdDk I think the title is self explanatory.
Nashimoto-P also has some songs about the darker side of the life.
http://youtu.be/ncqVZ6VqcK8 (alcohol abuse)
http://youtu.be/1mRvICojl20 (Self explanatory, though generally I think having a terminal illness could be something like this)
http://youtu.be/WxSmhDfuAxY (suicide)
I'm quite fond of these kinds of vocaloid songs as well, so if these are not enough I can list some more for you.
http://youtu.be/4RRvs_sDkRw (Abortion)
http://youtu.be/8ohG6nlpZWU (This one is tricky, personally I think it's about the circle of life and possibly reincarnation)
http://youtu.be/HinT8DXYdDk I think the title is self explanatory.
Nashimoto-P also has some songs about the darker side of the life.
http://youtu.be/ncqVZ6VqcK8 (alcohol abuse)
http://youtu.be/1mRvICojl20 (Self explanatory, though generally I think having a terminal illness could be something like this)
http://youtu.be/WxSmhDfuAxY (suicide)
I'm quite fond of these kinds of vocaloid songs as well, so if these are not enough I can list some more for you.