What is this dash-like punctuation at the beginning of lines, seeming to indicate rapid-fire thoughts?

Question

Here's a bit from a Kamoshida Hajime novel (Just Because!):

I've reviewed the Wikipedia article on Japanese punctuation as well as some related questions on this Stack Exchange but am unable to figure out what this dash-like punctuation at the beginning of each of these lines is, and how to type this. I've been using U+2500, BOX DRAWINGS LIGHT HORIZONTAL, for this because two of them combine nicely without any space inbetween (on all my devices and apps), like in the image:

──私、決めたから

Alternatives I've considered are: U+2015 (HORIZONTAL BAR), em dashes, and katakana continuation marks (though none of these combine perfectly without spacing?):

――私、決めたから (two horizontal bars)

——私、決めたから (two em dashes)

ーー私、決めたから (two continuation marks/chouonpu)

What's the right answer here? How should I properly represent this in text?

Answer 1

It's indeed a (long) dash. See:

• Is Japanese em dash equal to Latin em dash?
• Meaning of long horizontal bar in Japanese
• What does ー mean in this context?

It has several uses, but here, it is similar in purpose to 3点リーダー (･･･) used to add an emotional or reflective pause. Dashes are less common and thus feel somewhat literary. Perhaps these three sentences are monologues or lines imagined in someone's mind?

It's still difficult to reproduce this symbol outside professional-use DTP software like InDesign. See the first link above, too.

• The most traditional and conservative approach is to use U+2014 (EM DASH) twice. The 全角ダッシュ symbol in traditional Japanese encodings (0x815C in SJIS/CP932) is now mapped to this.
• You can also use U+2E3A (TWO-EM DASH), but this is a relatively new Unicode character and may not be supported by all platforms yet.
• The 全角ダッシュ was once mapped to U+2015 (HORIZONTAL BAR), but this is now considered a mistake (See: 全角ダッシュのマッピング問題). However, according to this article, this "horizontal bar" was initially intended to be used as a "quotation dash", so it may be a good choice in your specific case.
• Box-drawing characters like U+2500 are for making a table in a fixed-width terminal, etc. You should not use them to make a dash.
• By "katakana continuation marks", do you mean the long vowel marker (長音符)? Then you should not use it. It will render terribly () in serif fonts.