This character is a Modifier Letter and is mainly used in the Katakana script.
The glyph is not a composition. Its East Asian Width is wide. In bidirectional text it is written from left to right. When changing direction it is not mirrored. This katakana joins with other adjacent katakana to form a word. U+30FD prohibits line breaks before its position. There might be some exceptions, though.
The Wikipedia has the following information about this codepoint:
Iteration marks are characters or punctuation marks that represent a duplicated character or word.
Representations
System
Representation (click value to copy)
Nº
12541
UTF-8
E3 83 BD
UTF-16
30 FD
UTF-32
00 00 30 FD
URL-Quoted
%E3%83%BD
HTML hex reference
ヽ
Wrong windows-1252 Mojibake
◌ヽ
Encoding: BIG5HKSCS (hex bytes)
C6 DA
Encoding: CP932 (hex bytes)
81 52
Encoding: EUC_JP (hex bytes)
A1 B3
Encoding: EUC_JIS_2004 (hex bytes)
A1 B3
Encoding: EUC_JISX0213 (hex bytes)
A1 B3
Encoding: GBK (hex bytes)
A9 63
Encoding: GB18030 (hex bytes)
A9 63
Encoding: ISO2022_JP (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: ISO2022_JP_1 (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: ISO2022_JP_2 (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: ISO2022_JP_2004 (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: ISO2022_JP_3 (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: ISO2022_JP_EXT (hex bytes)
1B 24 42 21 33 1B 28 42
Encoding: SHIFT_JIS (hex bytes)
81 52
Encoding: SHIFT_JIS_2004 (hex bytes)
81 52
Encoding: SHIFT_JISX0213 (hex bytes)
81 52
Adobe Glyph List
iterationkatakana
digraph
*6
RFC 5137
\u'30FD'
Bash and Zsh inside echo -e
\u30FD
C and C++
\u30FD
C#
\u30FD
CSS
\0030FD
Excel
=UNICHAR(12541)
Go
\u30FD
JavaScript
\u30FD
Modern JavaScript since ES6
\u{30fd}
JSON
\u30FD
Java
\u30FD
Lua
\u{30FD}
Matlab
char(12541)
Perl
"\x{30FD}"
PHP
\u{30fd}
PostgreSQL
U&'\30FD'
PowerShell
`u{30FD}
Python
\u30FD
Ruby
\u{30fd}
Rust
\u{30fd}
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