So basically once upon a time, there was this woman named Emily Crane and she had a daughter named Lucy. One day there was a tragic accident involving a swimming pool which left Lucy in a coma. Before the accident, Emily had bought a stuffed animal for Lucy in hopes to give it to her for her birthday. But this stuffed animal is actually magic, and it grants the owner magical powers. However, since Emily had never actually given the toy to Lucy, it belonged to Emily and she then gained the ability to enter Lucy's dreams. Seeing that the child was frightened and having nightmares, Emily gave her the power to create a fantastical world inside her own mind for her to live in. The world and all of its inhabitants are brought to life through a combination of two types of magic; sun magic and moon magic which are both collected from the light shining on the river and harnessed by all. Also, note, time in this world passes much faster than the real world, so it's a Narnia-like situation. Emily is able to visit The Reverie every 'year' when really it's every night.
Ok so fast forward several months, and it's been many years. Over time, Lucy, now the Goddess Tempest, becomes corrupted, gaining control over the sun river to achieve the great powers associated with the sun. Emily has grown attached to The Reverie and vows to protect its inhabitants, but no longer associates with her daughter. Emily disguises herself by transforming into a nymph of sorts and changing her name to Ammil, so she can shapeshift between tree and human. She becomes a queen and her kingdom grows. One day she bears a son who she names Arbor. Tempest grows jealous of the Prince, and one night, learning of Ammil's secret, she kidnaps the young boy during the night with the intention of murder. The kingdom is in an uproar! War is waged in an effort to free the prince!
Thousands of soldiers march into battle against Tempest and her followers. Epic fantasy battle ensues! The prince is saved! But, there is a very high cost to this battle. Unfortunately, the vast majority of the kingdom is killed in action. Many children are orphaned, including Pirr. Spruce's family is a different story, however. Though her grandfather survived the battle, he spoke out against Queen Ammil's decision to wage war, and because of his opposition, he was banished from the kingdom.
Because of a shortage of older warriors, as soon as Pirr and Spruce became of age, they were appointed to be the royal guardians of Prince Arbor, swearing to protect him and the kingdom at all costs. So yeah, that's basically the whole backstory. you're welcome.