Similar to her previous world where after undergoing puberty, a young girl's ovulation took place around a couple of weeks before her menstruation period began, the same cycle was common in vampires as well.
However, there were a few distinctions that made it vary from the ones she had personally experienced in the past.
Unlike humans who experience menstruation every month, a female vampire would only ovulate and menstruate once a year.
'No more bleeding every single month!' Reina rejoiced when this memory popped up in her mind.
In her previous world, she was subjected to severe period cramps which made her dread that time of the month.
Therefore, to learn that she would not have to experience the same pain every single month in this life was making her feel better already, helping her concentrate on what she had discovered.
'The Krev cycle,' She recalled the name that was used in Rein's memories while referring to this biological phenomenon.
Once a year, a female vampire would ovulate for a whole week which allowed the male to impregnate her during this timeframe.
After this ovulation period, just like humans, if fertilization did not take place then vampires too would shed blood at the end of that week.
Immediately after the ovulation week comes to an end, a female vampire's period would begin and she would lose a large quantity of her blood for the next two weeks.
'Not only blood but she also loses half her life essence at the end of the period!?' Reina growled when the image of an exhausted Rein lying languidly on a bed appeared before her eyes.
Due to the loss of a large quantity of life essence, Rein would often need to rest and recuperate for a while before she can even move.
Reina had been rejoicing that she would have to menstruate only once a year but her joy faded instantly as this was beginning to look scary to her.
From what she had learned thanks to her predecessor's memories, she knew why this was so.
As the female's body needs an entire year's preparation for ovulation, once it fails, the energy put into this preparation begins to take a toll on her body, consuming a large quantity of her life essence.
If they got pregnant during ovulation, they would lose a constant stream of their essence to the fetus forming in the womb and if they did not then they would lose almost half of it all at once.
'Damned if I do and damned if I don't!' Reina scoffed at what she had just learned.
She felt especially incensed as one thing that she had learned through her conversation with the old man was that Rein already had a lower amount of life essence in her body as she survived on blood alternates.
To now realize that she would lose even that meager quantity of life essence once her ovulation period came to an end was further infuriating.
However, she could only press down on the grievances bubbling up in her heart and remain silent as she could not incur the suspicions of the King who was right next door.
She had not yet heard any sounds coming from the King's chambers which implied that he was still inside the Office adjacent to his room.
Though she could not listen in on what was taking place inside his Office, she had not yet heard the sound of his door being opened which gave her the confidence that she was right.
Rolling her eyes at the door, Reina decided to get back on track and not get distracted any further.
'So I ovulate once a year from now but I will be feeling worse than I did in my previous world?' She groaned and grumbled in her heart, making sure to not speak out loud for anyone who might be eavesdropping on her right now.
She had made the right choice as both King Zander and his aide were right next door and could hear everything being said in their vicinity thanks to their sharp sensory organs.
Dodging a calamity there, Reina's mind was once again directed on the matter at hand.
Since she now knew what she might experience when her period came, her next issue was to figure out when this would take place.
Glancing down at her well-developed breasts, she knew that Rein had been an adult for quite a while now.
Therefore, she should also possess memories of when this troublesome period of hers would arrive.
'Focus!' She shut her eyes and commanded her mind to search through Rein's memories to give her proper and useful answers.
She had already seen an image of Rein suffering during her period and chose to aim her attention on that image.
Thus Reina was currently forcing more memories to be triggered and hoped that she would succeed.
The last time she had tried this was when she had attempted to know more about Rein's family and her life before she met the King.
However, she could not gain any information and had been forced to stop on account of the insidious headache that had formed back then.
Therefore, keeping an eye out for any pain which might pop up abruptly, she carried on with what she had put her mind to.
It took Reina a few seconds to zero in on that particular memory and thankfully she felt no aches and pains this time around.
This encouraged her to pry deeper into Rein's memories and keep going until she found something useful.
Unlike the last time, this attempt had been a fruitful one considering how after a short while she had stumbled upon the memory she had been looking for and succeeded in triggering it.
'Oh, poor Rein…' She grimaced while soaking in the information she had gained from her predecessor's memories now residing in her mind.