Sultanate's ancient character appears in Book 1 (6)
I believe the answer is:
brunei
'sultanate's' is the definition.
(Brunei is an example)
'ancient character appears in book 1' is the wordplay.
'ancient character' becomes 'rune' (I've seen this before).
'appears in' indicates putting letters inside.
'book' becomes 'b' (abbreviation for book).
'1' becomes 'I' (Roman numeral).
'b'+'i'='bi'
'rune' inserted inside 'bi' is 'BRUNEI'.
(Other definitions for brunei that I've seen before include "major source of oil" , "Southeast Asian sultanate" , "Sultanate on the island of Borneo" , "State on Borneo" , "Commonwealth member" .)