The smallest print doing the largest amount of work
One hyphenated suffix, set small on a chest, carrying a relationship no single word in another language holds by itself. A badge-sized print that has to be walked up to.

-senpai. Actual reading size, on a hanger, nothing around it but a thin rule the exact width of
the word.
You have to get close to read it. That's not a printing limitation. That's the design.
Why does a hyphen do so much work here?
Because it announces, before you've read anything else, that this word is not standing alone.
A leading hyphen marks a suffix — a fragment that attaches to something. It can't be a sentence, can't be a name by itself, can't be shouted across a room the way a full word can. It exists only in relation to whoever it's stuck onto, and the hyphen is the one character that tells you that in advance.
What does the word itself carry that a translation would lose?
Rank, familiarity and address, folded into one suffix instead of spread across a sentence.
Swap it for the nearest word in another language and you get a title, or a term of respect, or nothing at all — because most languages don't have a single slot for "someone slightly senior whom I address with this specific mix of deference and closeness." The original packs all three into four letters and a hyphen. A translation has to either invent a clunky phrase to carry the same load or drop the nuance and hope the reader doesn't need it. Neither is really equivalent, which is exactly why the untranslated word keeps showing up instead.
Why does the print stay small?
Because a word this specific doesn't need volume, and blowing it up would misrepresent what kind of object it is.
This isn't a slogan meant to be read from across a street. It's closer to a name badge — something legible at conversation distance and invisible past it. Print it chest-wide in a display face and it becomes a claim shouted at strangers; keep it at reading size in a clean serif and it stays what it actually is, a word one person recognises and nobody else has to. A tag that quietly grew larger than its job makes the opposite move — this one stays deliberately small on purpose, and never grows.
Who decided this word shouldn't be translated?
No single person — it's a decision an entire practice arrived at independently, over and over, across decades of translators facing the same four letters and reaching the same conclusion.
Once enough translations in a row leave a term untouched, it stops being an individual choice and becomes an inherited default: the next translator doesn't decide to keep it, they'd have to actively decide to change it, and that's a much harder thing to justify. The word survives not because anyone ruled on it but because leaving it alone kept winning.
Does this only apply to one kind of relationship term?
No. Any culturally specific title, kinship term or form of address can end up in the same position — a word for an older cousin that isn't quite "cousin," a workplace title with no direct counterpart, a term of respect tied to a social structure the target language doesn't organise the same way. The suffix on this shirt is one instance of a much larger pattern: some relationships don't survive being renamed. A page of terms handled the same way, alphabetised is the same decision made eleven times over instead of once.
Can I use a real honorific from a real language?
Yes, in the sense that matters here — an honorific is a piece of a living language, not anyone's property, and using one accurately is simply using a word. What you can't do is lift a specific character's specific relationship from a specific published work and print it as a reference to that work; that pairing belongs to whoever created it, and it's licensable the ordinary way any character material is. The bracketed note plays the same permission game with a joke instead of a title — the device is free, the specific line usually isn't.
Does it print well?
About as cleanly as anything can. A single word in a clean serif at true small scale, one thin rule beneath it — flat ink, one colour, no gradient, no fine detail below the weave's floor. The whole design succeeds or fails on the type choice: pick a serif with enough weight in its thin strokes that it survives the fabric, and keep the rule genuinely thin so it reads as underline rather than bar. Works on light or dark garments equally, since it's one ink colour against a flat field either way.
How do I get one made?
Describe the word and the relationship it carries at JustOG. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
Four letters and a hyphen, and somewhere a whole relationship fits inside them.