One day when Halo invited Venus to her mansion, Uno barged into the house and demanded a pony. After a huge argument earlier in the day, Uno ran away from her father because he said she could not have one. Their parents finally gave in to her demand in fear that she might try to runaway from them again. And why shouldn't she have one? They certainly can afford it. Venus, who just happened to be sitting on the couch, asked for one as well not because she's a spoiled brat, but because she was excited about ponies. She of course did not expect it. Halo being a close friend of Venus's father Jupiter decided that Venus should have one as well and so she did. They named the horse Diamond, and then gave it, and Uno's pony, a large field encricled by a fence. Venus wasn't exactly the best caretaker for the horse so the horse meets with an unfortunate end. Diamond appears in Volume 5 and then again in Volume 6.