If you have already downloaded the zip file in post #154, you may need to download it again. As
@Pieter Boelen suggested, I've added "RESOURCE\INI\TEXTS\ENGLISH\Storyline\OnePiece\QUESTBOOK\Beginning.txt" and re-uploaded it.
That is a questbook. You can edit the "text.t1" line to whatever you like. You can add more lines - "text.t2", "text.t3" etc. Look at "quests_reaction.c" to see how the file is used.
SetQuestHeader opens the book,
AddQuestRecord copies a line from the file into the questbook, and when the quest is over,
CloseQuestHeader closes the book. All of them use the filename. The "title" line in the file is often the same as the filename, but does not need to be the same, as shown here. (You can also look at the "quests_reaction" file in other storylines to see how they use these lines.)
After the "text.t1" line is a blank line. There always needs to be a blank line after the last "text." line - it was found that without that blank line, the questbook as seen in the game has random rubbish added to it. With the blank line, no such rubbish appears. So, if you add another four lines for example, then you don't need a blank line after each one but you do need it after "text.t5".