Material chapters are basically the details that aren't directly told to players in the gameplay or cutscenes, but can be pieced together if you go digging around in flavour text.
A crest is the manifestation of power granted by or from another, more magical entity. Crests generally refer to the power of a dragon, while a Brand is more commonly used for the power of a laguz clan. In everyday language, the two terms are interchangeable in most places. Some Divine Dragon worshippers will also refer to crests as 'holy blood'.
A crest's power does not need to be granted voluntarily to function. Indeed, many beorc in the past have sought to kill dragons in hopes of obtaining this power – usually by consuming parts of a dragon's body. As the golden age came to an end and most surviving dragons went into hiding, the origin of crests was largely forgotten, while those families who did hold crests tended to use that ability to cement themselves in positions of great power.
The Brand of the Exalt, is more accurately described as the Crest of Naga. This crest is easily the most famous in modern Archanea, as it also serves as the mark of legitimacy for the royal family of Ylisse. With Naga enshrined as the chief Goddess of Ylisse, her crest grants the wielder immense strength, healing, and use of the Falchion. Mastery over the Crest of Naga will allow the wielder to summon the flames of [Aether].
While many people have come to view the visible manifestation of the crest as a measure of legitimacy, or divine favour, the truth is that all first-generation descendants have access to the crest in full, regardless of if it is visible on the body. As evidence that Naga is watching, any royal branch family's crest will fade into a dormant state within two generations. Ylissean history has proven this tactic to greatly reduce the chance of wars of succession from breaking out, when compared to former Archanean kingdoms.
AN
[Aether] (skill/special)
Combines the effect of Sol and Luna = Increased penetration plus lifesteal
Not to be confused with the liquid you fight for in FEH Aether Raids.
FEH has made it clear that [Aether] is granted only to Chrom and Lucina – those who have mastered their Naga-blessed bloodline. On the other hand, [Radiant Aether] belongs to Ike, who accomplishes the same effect but through different means.