Here's a quick guide to Safiiru and Petz (Sapphire & Prisma in the dub).
Safiiru and his brother Demando (sp?) (Diamond) wanted to get revenge for the banishment of their ancestors from the Moon to the planet Nemesis. They were known as the Black Clan. The power of the Dark Crystal (not related to the movie) was given to them from an evil being known as Wiseman.
Petz was one of the sisters that worked for the Black Clan. She was the most evil of them at the time, even hurting her own sisters (although that was possibly the because of the power rod Rubeus gave her). Eventually, she realized she was being used, and Sailor Moon healed her. However, apparently even when she was evil, she still loved Safiiru.
Much later Safiiru realized that Wiseman was just using them, but couldn't convince his brother. When Wiseman attacked him, he went to Earth to warn his brother, but Petz found him first and tried to nurse his wounds. She also taught him that Earth was full of love, and made him question his beliefs about the Earth. Safiru confronted his brother, but while he was telling him what he saw of the future, Wiseman killed him.
When did Safiiru and Petz have time to conceive Jian-wa? I don't know. But they did spend a few hours together before he left. And who knows what they did before she left the clan. And when his jacket disappeared into a sparkling cloud when he died, Petz said something to the effect of him always being inside her.... So read whatever you want into that.
(<Giggle, giggle> Just realized that both Mi-chan and Neko's dates had Megumi Ogata as a "mother" (Haruka and Petz). It's fun to listen to Haruka's voice in another SM character.)