Why are 关 and 复 half-width in Japanese?

Question

关 and 复 are the simplified Chinese forms of 關 and 復複覆, respectively. Usually simplified Hanzi that don't exist as kanji don't get any special treatment and Japanese fonts might not even display them, such as this one 简. However, not only do Japanese fonts support the glyphs, but they even display them as half-width. Every other cjk standard displays them as fullwidth.

My first guess was that the characters were somehow already in Japanese as kanji radicals (忄 for example isn't full-width), but they aren't considered radicals or even components. If you look them up on Jisho they even have meanings (if not pronunciation).

All of which begs the question, if 关 and 复 were recognized as kanji, why are they not full width like every other Japanese character? And if they aren't, how did they get into Japanese in the first place?

Answer 1

EDIT: With some more research, I found the reason. As I expected, it's due to historical unification of JIS X kanji with Unicode codepoints. Here's a GitHub thread about the issue, including precisely the two characters you asked about.

The tl;dr is that the Japanese codepoints corresponding to those characters, which were unified with the Simplified Chinese characters, were narrow to begin with, and so have stayed narrow in Japanese rendering in order to stay compatible.

Check out Ken Lunde's answer:

The Japanese (JP) forms of U+5173 (uni5173-JP; CID+11297) and U+590D (uni590D-JP; CID+14484) are intentionally narrow (they correspond to Adobe-Japan1-6 kanji, which in turn correspond to JIS X 0213:2004 kanji, specifically 2-03-08 and 2-05-27, respectively), and are referenced only by the Japanese and Korean subset OTFs and Japanese and Korean OTC font instances. (Note that these characters do not correspond to hanja in KS X 1001 nor KS X 1002, so the Korean subset OTFs and Korean OTC font instances are merely inheriting the default glyphs for Japanese, which is by design and intentional.) They are also the default glyphs for the multilingual OTFs because Japanese is the default language. If you check other Japanese fonts, you'll see similarly narrow glyphs for these two characters.

As to why: I could only venture a guess -- perhaps they were construed as character parts in Japanese digital fonts; since these characters do not properly exist in Japanese, just like 艹 or ⺝, they therefore don't have a "proper" square rendering.

The CJK Radicals Supplement section of Unicode has many other radicals whose rendering doesn't quite look "square", because they are used to describe parts of full characters, without being full characters themselves.