"Good morning, everyone! My name is Kisuke Urahara! Some of you may have heard my name before, but for those of you who haven't, I'll start with a brief introduction. I began as a lesser noble of the Shihoin Clan, and as such, I joined the Second Division early on. I was later promoted to Captain of the Twelfth Division, and became the founder and first head of the Shinigami Research and Development Institute. I was framed by Aizen and exiled to the living world during the Visored incident. I became a shop keeper in the living world and kept an eye on things, and personally trained Ichigo Kurosaki as a Shinigami. I helped in the final defeat of Aizen. I collaborated with Captain Mayuri during the Quincy invasion. After the war, I helped Uryu Isshida and his father establish the Delta Division to prevent further wars between our differing cultures, and I now serve as an ambassador on behalf of the Shinigami. Now, I've been asked to fill in as your professor for a few weeks while Kukaku Shiba is dealing with some family matters."

The blonde man stood at the front of the classroom, smiling casually at the students seated before him. Although he had taught many individuals, and even led his own division for a time, this was a new experience for him.

"The thing is, I was supposed to spend the last few days creating a lesson plan, but I got caught up in an experiment I was very anxious to see completed, so I am going to have to sort of make this up as I go along. I really don't have any sort of requirements for what I cover, so if any of you have questions, I probably have some sort of answer. It would be an easy way for me to get an idea of what I should talk about for the rest of my time as your teacher. So... What do you want to know?"

Urahara looked around the class room. The students seemed slightly lost by his eccentric opening. Hesitantly, one student raised her hand.

"Miss Izumi, ask away!" The substitute professor grinned as he gestured to the raised hand. He had made it a point to memorize the names and faces of all of his students in the minutes before class.

"I've heard a lot of gossip and rumors that Kurosaki and Kuchiki are expecting a child... Since he is Shinigami, Hollow, and Quincy, and she is only Shinigami, what would their child be? I don't think such a thing has ever happened before, has it?" The girl asked. Several of the students siting near her nodded, also curious about the upcoming birth of their hero's child.

"Ah, that is a really excellent question to get us started! Ichigo Kurosaki is, after all, one of the most well known and least understood men to ever live and die. So, over the next weeks, I will endeavor to explain some of the intricacies of his existence, along with that of his future child. Spiritual Genetics are an advanced topic not normally covered in the academy, but I think you can all handle it!" Urahara turned to the white board at the head of the room and wrote two words with a line dividing them. 'Life' and 'Death'.

"A good place to start, and a fundamental question that scientists and philosophers have struggled to answer for thousands of years... What does it mean to be alive? Anyone have suggestions? What does it mean to be alive? Can you define it? What about death? Go ahead, say whatever you think, and I'll do my best to write down everything I hear!" Urahara listened as the first few timid suggestions quickly turned into a storm of ideas ranging from mundane to wild and crazy.

"Breathing!"

"Heart beat!"

"Movement!"

"Alright, alright, that's enough for now! These are all wonderful ideas! It seems that you have hit on almost every single theory that has been suggested over the years. So, allow me to present my theory." Urahara turned to the board and drew a few pictures. A rock, a wooden plank, and a cat. He turned back to the class. "Now, which of these is alive?"

"The cat!" The class chorused back to him. He nodded.

"Yes, the cat!" He drew a ghost next to the cat, and a lit light bulb next to that. "There are five objects up here now. Only one is alive. But what really sets the cat apart from the ghost and the others? The light bulb takes in and converts energy to another form. It also radiates heat. The ghost has most of the typical life sustaining functions. The rock can grow with sedimentation or split into new rocks. Perhaps it will become more apparent when I tie it to Aizen's plot."

At the mention of the infamous former captain, the class's full attention focused and tensed. Not enough time had passed yet to ease the pain of what he had done and what he had tried to do.

"Aizen said once that Shinigami have a limit. Every last one of us. There is a maximum to what we are capable of. And no matter what we do, no matter how much training we undergo, we can never exceed that limit. He wanted to use the Break-Down Sphere to remove that limit. To become something beyond Shinigami or Hollow. However, his plan was fundamentally flawed. Because even a being that has transcended both Shinigami and Hollow is still dead. It will still have a limit."

He drew a hammer on the board.

"When the rock is broken, it is broken. It has a limit. It can only take so much abuse before it breaks. The plank, also, will break under a certain amount of weight. The ghost, like a Shinigami, has a limit. A finite potential. The light bulb, once shattered, makes no more light. But the cat... If you strike it with the hammer, you break it. But it will heal. So will the ghost, to a point, but the difference is, once broken, the cat will grow back stronger. It will advance and surpass itself. That is life. Life is limitless. Life is the potential to have infinite potential. Life is the ability, when faced with adversity, to raise ever higher. And that, more than any natural power from genetics or luck or fate, is why Ichigo Kurosaki became so powerful. Because his powers emerged while he was still alive, he was a Shinigami with no limit."

"Does that mean he is as strong as he will ever be now?" One of the students asked. "Since he has left his body permanently?"

"That is hard to say. It could be, that now he is no longer part of the living, he is limited, but it is also possible that his spirit is so powerfully full of life that he will never reach a limit.