Growing as a Familiar

You wake up inside an egg that is nearing its hatching. You hear voices outside of the shell. Something about being chosen. When your egg is chosen you hatch revealing that you are an F rank beast, the weakest of familiars, and now the chosen familiar of the student who chose your egg. You are now the familiar of a teenager who is in an academy focused on raising magical beast familiars. The only way for you to become stronger, gain skills, and increase rank is to train hard, and take the mana of creatures that you and your partner hunted and killed. Your goal? Become strong enough to protect your person by the time you are fully grown and they graduate.