Verified answer

Power mad, Hougyoku was meant for raising power of shinigami against ever more powerful hollow yet it became something that was able to breakdown the barrier between shinigami and hollow and also raise reiatsu to such a level that it overwhelms the senses just like being a vizard and training in your inner world while in bankai does as it had accidently become a spirtual being that fed off it's handlers desires and it was important for it to be inside rukia so it could be protected...... at least that's how i saw it.