After Black Zetsu reunited with Princess Kaguya, he practically became her devoted lapdog. Whenever she gave an order, he rushed to carry it out without a moment's delay. Though she treated him like a servant, he seemed to enjoy every second of it.
Princess Kaguya was delighted with this son she had created from her own will. Unlike her two ungrateful sons who had betrayed her, Black Zetsu understood whatever she wanted from the slightest glance and fulfilled her wishes perfectly. Princess Kaguya had completely surrendered herself to the pleasures of eating, drinking, and having fun.
As for gathering chakra?
Whoever wanted to do it could go ahead. She certainly couldn't be bothered.
After experiencing the allure of the Otherworld's magecraft firsthand, Aizen, an ambitious schemer and scientist, threw himself into studying it. He intended to incorporate its system into the incomplete Hōgyoku he had only recently created.
Paracelsus was fascinated by this power, which could fulfill its host's desires by bringing them into reality. The Hōgyoku's abilities somewhat resembled the Root of the Nasuverse, so he joined Aizen's experiments to modify it.
Naturally, Aizen warmly welcomed the founding father of alchemy. After exchanging their knowledge and experiences, the two began researching how to perfect the Hōgyoku's structure.
Ever since Princess Kaguya had thrashed Madara Uchiha and Hashirama Senju, and Sasuke Uchiha had then told them she was the Progenitor of Chakra, the Sage of Six Paths' mother, and their grandmother as the previous reincarnations of Indra and Asura, the two had withdrawn into themselves, training like mad every day.
But both had already reached the peak of their strength, leaving little room for further improvement unless they devoured the God Tree and became Ten-Tails Jinchuriki. Kenos was still working to overcome the difficulties of combining tailed beast replicas into