Anime - twin sisters turn the people they defeat into crystals. Twin nieces are born

Question

In this anime twin sisters have powers and whosoever they defeat turns into a crystal. Both sisters are trying to kill each other because one sister was evil/jealous, at the climax both sisters stab each other but one sister had just delivered twin girls so she ends up turning into crystal, the surviving sister forgives the dying and adopts her nieces and then goes to hibernate and deep sleep while her friends take care of the twin nieces.

Answer 1

Might this be Blood+?

The series is initially set in September 2005 in Okinawa City (Koza) on Okinawa Island near the US Kadena Air Base. Under the care of her adoptive family, the protagonist Saya Otonashi had been living the life of an anemic amnesiac, but otherwise ordinary schoolgirl. However, her happy life is shattered when she is attacked by a Chiropteran, a hematophagous bat-like creature that lives by feeding on human blood. Saya learns that she is the only one who can defeat them, as her blood causes their bodies to crystallize and shatter. Armed with her special katana, Saya embarks on a journey with her family, friends, allies, and her chevalier Haji, to rid the world of the Chiropteran threat and recover her identity. The course of the journey reveals the background history of the Chiropterans and Saya's mysterious past, which extends into the mid-19th century. Over the course of the series, Saya travels across the world from Japan to Vietnam, Russia, France, the United Kingdom, and finally the United States.

From this character list:

Diva (ディーヴァ, Dīva) is Saya's younger twin sister and the main antagonist of the series. In 1833, Joel Goldschmidt discovered the mummy of an unknown creature that had two cocoons that reacted to human blood. Diva was born from one of these cocoons. As an experiment, Joel separated the twin girls, raising Saya as if she were his own daughter, while Diva, who was given no name at the time, was locked in a tower and given only the basic necessities to live by Joel's assistant, Amshel. In 1863, Saya discovers the girl locked in the tower and names her Diva. Twenty years later, Saya releases Diva from her tower so that she can sing at Joel's birthday party; however, Diva murders Joel along with the rest of the people attending the party before fleeing the area.

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As a result of her attack on Riku, Diva becomes pregnant. She does not give birth for over a year, when Amshel cuts the cocoons out of her body. Diva seems to treasure her babies and care for the cocoons. At the Metropolitan Opera House, Diva is set to perform a live broadcast that would cause much of the world's population to turn into chiropterans. The Red Shield and Saya are able to stop the broadcast, and the sisters have their final battle, while Diva's chevalier Nathan watches nearby with the babies. The fight ends as Diva and Saya pierce one another with their swords, which each had been coated with their own blood. Saya is unharmed by the attack, due to Diva's blood having lost its power when she became pregnant. Diva, on the other hand, begins to crystallize from the effects of Saya's blood. Her babies do not emerge from their cocoons before Diva reaches for them, with a vision of herself with her daughters.

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After Saya kills Diva, [Kai] is able to convince her to continue living, which prompts Hagi to "disobey" Saya and confess his own love for her. Saya and Kai return to Okinawa and reopen their late father's restaurant. A month later, Saya goes into her hibernation cycle, and Kai puts her in the family crypt to sleep. As per his promise to Saya, he raises Diva's daughters as though they were his own. Together, they regularly visit Saya's resting place to keep an eye on her while she sleeps.

Trailer

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