Since I'm not very good at English either, I enlisted the help of Deepl and “Mirai Translation https://miraitranslate.com/trial/”.
I inferred that the request was to have consecutive footnote numbers for the footnote section due to the vertical writing,
so I looked into it using [manyfoot.sty][1] manyfoot.sty as a reference.
Before presenting the proposed solution, note that \FootnotetextA{}{#1 #2} is written as % This works!,
but since the footnote number (specified as alph in this case) is not displayed, characters like a or b are not shown.
Is this the intended behavior? If so, the following discussion becomes irrelevant.
Nevertheless, assuming the footnote number should be displayed as usual, here is the proposed solution.
Since \DeclareNewFootnote is declared, \FootnotetextA is being used.
Referencing the URL manyfoot.sty, using \footnteA allows the footnote number to render as a sequence number without needing the \rensuji macro. How about trying the following?
diff --git a/example.tex b/example.tex
index 02faa10..d85f5fd 100644
--- a/example.tex
+++ b/example.tex
@@ -11,12 +11,15 @@
\newcommand{\mynote}[2][]{%
\stepcounter{mynotecounter}%
\def\temp{#1}%
\ifx\temp\empty%
+ \message{DEBUG in mynote T-side 「\temp」「#1」「#2」}
\FootnotetextA{}{#2}%
\else%
- \FootnotetextA{}{{\linenumberfont\rensuji{#1}} #2}
+ \message{DEBUG in mynote F-side 「\temp」「#1」「#2」}
+ % \FootnotetextA{}{{\linenumberfont\rensuji{#1}} #2}
% \FootnotetextA{}{#1 #2} % This works!
+ \footnoteA{#1 #2}% <================= LOOK THIS LINE
\fi%
}
If the above is acceptable, it might be possible to define it more simply like this:
\newcommand{\mynote}[2][]{%
\stepcounter{mynotecounter}%
\footnoteA{#1 #2}%
}