The criminals at the hospital are after the Male Essence meant for GoroAfter all, what could make things worse for Goro then not getting a complete transfer, if she gets any at all? Note that all the criminals are female as well.
The reason Tanica didn't die right away after ripping her lifeforce out was because the seed kept her alive until it released her.Looking at Tanica through Chapter 13, her condition remains about the same from Page 21 (just before tearing out the lifeforce) to Page 27 (after having kept Goro alive until morning) to the beginning of Page 30 (when she sees Goro and Aki together) ... and degenerates severely over the three minutes it takes for Sarin and Mori to prepare the egg afterwards. On Page 37, Sarin says that the seed released him when he had accepted his fate and let go of himself. Well, Tanica tore out her life because she believed Goro's life with Aki was what was worth throwing her life away for — and a Heroic Sacrifice is pretty much the exemplar of accepting your fate and letting go of yourself. She didn't start decaying from lack of life force until the morning because it wasn't until that moment that she knew whether she had succeeded or failed.
Sarin/Tanica's seed encourages Generation Xerox.Of the mentor variety. We never get to see Sarin's mentor's hair color, but it was probably green, and Sarin's mentor likely went through a similarly-hard childhood, was turned into a tree by the seed of a previous 'victim', and turned his life around after that. We don't know what he did, but it was probably benevolent and he was clearly skilled with transformation magic. Fast-forward to him seeing Sarin walk the same path, and Sarin goes through similar redemption, gets trained, and becomes a total magical badass who is certainly benevolent and is one of the best at transformation magic. Sarin already has many of the same qualities as Sarin's mentor did. Now come to Tanica, whose similarities to Sarin have been noted. They both were walking down a bad path, only for the seed to instill a Heel-Face Turn in them. Tanica (now as Elka) has been turning her life around since then, already showing great signs of benevolence. It's basically canonical that she's Sarin's apprentice (although she is around several other powerful doctors, Sarin is her main influence), and has within her incredible power. The people are not exactly the same each time; Elka's ultimate gift may be related to transformations, but her own "gift" is going to be different from Sarin's. So how she uses her powers will ultimately differ. But the path is already laid out. A powerful potential wizard, transformed by the seed from a bad life into a better one, with the desire to help others, being trained by a powerful wizard that has great skill in transformations.