It had been a full year after Ichigo had lost his Shinigami powers using Mugetsu, which he had not only regained his own powers, but was able to use Mugetsu now without loss of Shinigami powers, thanks to help from the help of Uhara, who had pushed him hard, at times beyond his limits. The minute he did regain his powers, he found a nagging, feeling in his chest that wanted him to go back to Hueco Mundo, even with Aizen dead.
This day, he caved into those desires that had been increasing every day. He had gotten permission to use the Seireitei from the Head captain Yamamoto, and he noticed as he had stepped foot back into the barren desert called Hueco Mundo, that he was looking for someone, without idea of who. Ichigo wondered, "Have I forgotten someone here?"
He did occasionally find a hungry hollow, which he put down with a single swipe of his zanpakuto. He passed the place he had fought Ulquiorra, and counted his lucky stars he lived past that day. Something in his mind was stirring, but he did not know what.
He encountered the place Nnoitra had almost taken his life, and as he reminisced about the event, he knew the exact person he was looking for: Neliel Tu Odelschwanck, the turquoise-haired Espada that had saved his life that day by regaining her powers and fighting Nnoitra.
He sensed the Spiritual Pressure of an Espada, and started running. He felt that it was the tres Espada, Nel, the one he was looking for. He began running, flying towards it. There were still the signs of his fight with Grimmjow, and on the pillar her and Orihime were standing on during that fight,stood the Espada his heart was yearning for: Nel, who had regained her true form. She knew he was coming a long way off, and when Ichigo was a foot behind her back,she turned, and with a sweet smile, "Hi Itsygo!"
Without even consent by his mind, he kissed her smiling lips, and to his surprise, she blushed as she kissed back. He was startled as he realized his actions, and jumped back. " I-uh I-I don't know wh-what got into me, Nel, I'm s-" Neliel silenced him with another kiss, and the tension in Ichigo's body faded as he embraced her soft embrace and returned the passionate kiss Nel was giving him.
"Itsygo, last time we were together, I didn't know either. But when you left, my heart craved your company. I tried to restore my life before you, even fixing my mask, thinking that if I did that, my heart would stop yearning for your company. But it only increased, day by day."Neliel said, with an affection expression across her still-scarred face, and it kept that pink mark that went cheek to cheek. "I guess you were the first person to eve show love to me, even if it was just as friendship, but I noticed how you still wanted to protect me when I decided to protect you."
They hugged, and as both the hilts of their Zanpakutos met, they felt a small twitch on the back of their hand, for Ichigo it was on his left had, and for Nel it was on her right. And this hug wasn't as powerful as her usual, it was soft, relaxing. He later made it to Nel's humble abode, and made contact with the soul society, and Neliel was granted permission to enter both the world of the living and the soul society, with the condition that she must be within half a kilometer of a Shinigami, which would not be an issue as she had some money she would use to get a gigai and a house in the world of the living.
Ichigo later noticed the brilliant blue tattoo on the back of his hand, and without a word on Ichigo's part to ask what it was, she explained. "When an Espada an another being, Espada, Vizard, Arrancar, Shinigami, or anyone else who uses a Zanpakuto, falls in love with them mutually, and their Zanpakutos meet in a peaceful manner, it forms what we call a 'Unison Mark'. You powers, Itsy, are now mine, and my powers are yours, but we also keep our own. It's like we are just one being, especially since we now feel what the other feels. Let me demonstrate, Itsy." She went to her refrigerator,opened the freezer, and touched an ice cube with her index finger. Ichigo felt a cold sensation on his finger, just like he was expecting.
That night, they stayed at Nel's house in Hueco Mundo, so they would be well rested for their journey to both the Soul Society, and The World of the Living.