Senzu Beans are a seemingly mystical beans with immense rejuvenative properties in the Dragon Ball and Ed Edd n Eddy Z franchises.
The Senzu Beans were mass produced during the School Wars in order to even the odds, with the militaries unable to heal the injured faster then the Teachers could rebuilt their droids. In some incarnations of the series, it was actualy Son Goku that gave the first seed to a Senzu Tree to the Neo Earths Special forces in order to allow them to grow them. When eaten, the users wounds and vitality is instantly restored. For Saiyans near death, this often brings about a power increase as per the nature of their race.
In some incarnations of the series their also existed an entire farm of Senzus, a true lifeline to the army. In these continuities the farms most likely still exist, possibly belonging to G.U.N.
Once the School Wars ended, the NESF members took their own seeds for Senzu Trees in order to use in their training and crusades to keep the world safe.
Supposedly of the two cousins present in the Heritage saga it was Drew who had Senzu Beans, as the Eds had no idea what they were despite being trained by Corey. Implying Corey did not have any on him while at Peach Creek.
Senzu bean are used throughout the series by the heroes in order to heal their wounds after battle. It is also notable that they often burn through their reserves during training, leaving barely any for the true battles.