After reading a popular science article, I found too many basic errors, so I might as well write one myself.
々 - Repetition Character for Kanji#
Repeats the previous kanji, originating from ancient Chinese. For more details, you can refer to previous posts:
Repetition Characters and Simplification of Kanji
Research | How to Read 壱 / 雫 / 栞 /々 in Chinese?
ゝヽゞヾ - Kana Repetition Symbols#
Repeats the previous kana, using 「ゝ」 for hiragana and 「ヽ」 for katakana.
「ゞ」and「ヾ」are used as repetition symbols when there are voiced marks.
When the previous kana has a voiced mark, 「ゝ」still represents the unvoiced kana, while「ゞ」represents the voiced kana, and vice versa.
〆- Shime, Japanese-made Kanji#
Japanese-made kanji (cursive style?), derived from the cursive form of the kanji for "占める" (shimeru), later expanded to represent other homophonic kanji (shime), such as "締め，" meaning final, seal, conclusion, etc.
ゟ - Yori#
A contracted kana, phonetically and semantically derived from "より" (yori).
ヿ - Koto#
Similarly, a contracted form of the katakana "コト" (koto).
ヶ - Small Ke (ke)#
Originates from the variant "箇" (ka) of "個" (ko), abbreviated (upper left component).
When used as a counter, it has the same usage, pronounced "ka," for example:
1 ヶ月 / 1 か月 / 1 箇月
And more variations:
1 カ月 / 1 ヵ月 / ケ月 / 1 個月
In romaji input methods, "xke" is used to input small kana.
Additionally, it is also used in proper nouns like place names, pronounced "ga," replacing the auxiliary verb "が" (which can be understood here as: of, a remnant of ancient Japanese), for example:
関ケ原町
Generally translated as "of" or left untranslated.
〼 - Phonetic: Masu#
The 〼 symbol comes from a square measuring vessel used for measuring sake: the kanji is "枡" (a Japanese-made kanji), pronounced (masu).
Here, it is only used to indicate the polite ending "ます."
卍 / 卐 - Manji#
This is a kanji, and its current meanings largely derive from Buddhist symbols.