This was an engaging, intense read. Both the magical core transplant and the One True Love were fascinating concepts, and I really liked how you used them to get Severus and Harry together. The overall effect was romantic, yet not completely angst-free. Also, the alternating viewpoints worked very well in establishing their situations early on, and I really enjoyed getting to know how each of them felt about what was happening. Two of my favourite bits:
The mystery was solved when a small group of house-elves had emerged from the shadows the first day he and Harry took possession. Severus had been mildly disgusted as he watched the diminutive creatures fawn over his blushing lover, startled to find a hint of jealousy in himself over the adoration.
Without hesitation, the dark wood rose into the air and flew to Severus' hand with a resounding slam. McGonagall snorted softly, the sound halfway between a laugh and a sob, and while elation filled Harry, it was the look of incredible joy on Severus' face that brought him to tears. Throwing himself across Severus' chest, their hearts beating against each other, Harry let all his fears bubble away and all his hope for a future come together as he was held tightly.