D is a pill created by Dr. Aris specifically for use by the DA-5 and herself. It is a small, gray pill that enhances the strength, speed, and overall ability of the user when it is consumed. The secondary purpose of the pill is that it lets (should an emergency arise) Krantz or Dr. Aris absorb the life energy of one of the members of the DA-5 with greater efficiency so that they can become powerful enough to overcome or escape any potential foe.
When analyzing the pill, Frankenstein discovered a side-effect that causes the users' cells to deteriorate, shortening their life-spans. Frankenstein has since replicated D and removed it's side-effects. He created two different types of pills based on the original D. One of those pills does not have any of the harmful side-effects, but gives a much smaller power (about 30%) increase. The other one of Frankenstein's prototype D pills was consumed by Dr. Aris and is responsible for the coma that she is currently in. That prototype was meant to replicate the effects of D with a 200% increase in power compared to D, but with the side effect of an imminent death. The new D are created separately for Tao and Takeo, and if someone else consumes it, their body will break down.
After being allowed more time to research about D and the bodies of Tao and Takeo, Frankenstein gives the duo another pill, called T-2 (named after Tao and Takeo). T-2 is a lot more stable and effective than the previous pill Frankenstein created and also has good taste (strawberries)!! These pills are also suited for Tao and Takeo only and turns their skin to a darker blue colour than D.