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 the previous posts:
Repetitive Character Symbols 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, with hiragana using 「ゝ」 and katakana using 「ヽ」
「ゞ」 and 「ヾ」 are used as repetition symbols when there are voiced sounds.
When the previous kana has a voiced sound, 「ゝ」 is still used to indicate the unvoiced kana, while 「ゞ」 indicates 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" (to occupy), later expanded to represent other homophonous kanji (shime), such as "締め，" which means final, seal, ending, etc.
ゟ - Yori#
A contracted kana, phonetically and semantically derived from "より."
ヿ - Koto#
Similarly, a contracted form derived from the katakana "コト."
ヶ - Small Ke (ke)#
Originates from the variant "箇" of "個，" 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 such as 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 sentence ending "ます."
卍 / 卐 - Manji#
This is a kanji, with its current meaning largely derived from Buddhist symbols.
ゐ / ヰ - Wi (wa-row i)#
Historical kana, whose pronunciation has merged into "i" in modern Japanese, thus discarded.
Still used in classical literature and some artistic works.
ゑ / ヱ - We (wa-row e)#
Similarly,
Historical kana, whose pronunciation has merged into "e" in modern Japanese, thus discarded.
Still used in classical literature and some artistic works.
(Various Historical Kana Usage.jpg)