[quote=@Databug]
How exactly does someone receive their grimoire?
What's the political structure like in this region?
What are devils like in this setting?
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Hello and welcome! In Black Clover, a Grimoire is essentially a spellbook that automatically seems to update itself as the user grows and develops their magic. Magic can be used without a Grimoire (think starting a campfire, watering a garden, or telekinetically manipulating small objects for daily life) but in order to use more advanced and powerful spells, the book is seemingly needed to control and channel the Mana.

When every child in the Clover Kingdom (and presumably in other nations of the setting) turns 15, they are able to attend that year's Grimoire Acceptance Ceremony, which takes place inside large Library Towers around the kingdom. So far, it's not known even in canon how the grimoire system came to be, if the books are made by someone, etc. But as spells appear inside them in a runic script, it allows the mage to better use their own magic at a much more powerful level.

The political structure seems to be that of either an absolute or constitutional monarchy. There is a Clover King, who is the head of government; the Magical Parliament, which is the legislative and judicial branch of the kingdom and seems to be run by members of the nobility; then there is the Wizard King, who is to the Clover King what a Shogun would be to a Japanese Emperor, essentially the highest military power of the land. The Wizard King operates as the head of the Magic Knight Squadrons, and directly beneath him are the Captains of the 9 squads.

The Nobility are those who, from olden days, have accumulated both wealth and magic power. Compared to the Commoners (peasants, serfs, etc), they are usually born with more inherent magical ability and, in the canon series, often look down on the commoners who have less. Because this is a "sequel" styled RP, this discrimination has lessened to a degree, but there is still very much a difference in the social classes.

Because your question about Devils requires some things to be revealed that are later in the series, I'm gonna put it in a hider. I tried to give sort of a "generic overview" that doesn't outright reveal any story secrets, but there could still be spoilers.
[hider=POTENTIAL SPOILERS: DEVILS]In Black Clover, "Devils" are creatures from the Underworld that we don't yet know everything about. The Underworld itself is a parallel realm, and has been possibly implied to be the "realm of the dead." It seems to be a very barren land in any case, and the Devils born there have nothing better to do than torment each other and sort themselves into a hierarchy, which is also defined by magical power. Normally, however, Devils cannot pass through the Underworld Gate in order to enter the Living Realm. Humans, however, can use Forbidden Magics to communicate with and potentially summon Devils. 

In order for a Devil to use its magic in the Living World, it must first corrupt another being capable of using magic, then when the corruption is complete it can possess that person and take their grimoire for itself. Devils can also form contracts with humans but, depending on who the contract favors, in the vast majority of cases it doesn't turn out well for the human party. The only real "motives" seen in most devil's actions is simple self-amusement or hunger for power, manipulating and hurting others just because they can out of sheer malice.[/hider]