Yes, rōmaji is used by Japanese people, but mainly as design elements. Elementary school children learn to read and write rōmaji in the 3rd grade, and virtually all adults can understand Japanese words written in rōmaji. Latin alphabet often strikes Japanese speakers as cool or modern. You can find Japanese words represented in rōmaji on T-shirts, mugs, ...
EDIT: It turned out that OP did not know most kanji have multiple readings in Japanese. He is actually trying to get the reading of words (e.g., 生地 → K, 生卵 → N, 生命 → S, 生霊 → I). For this purpose, a word-based dictionary is needed. There are several open source morphological analyzers that can do the job and more (kuromoji, mecab, Kagome, etc). See also: Is ...
Is this a thing ever done in Japanese text
If you specifically mean "replacing B/C (and only B and C) with the red/squared emoji 🅱️", then, no, that has never been a thing in Japan. I did not know such a phenomenon until today, and its cultural background (according to this) is not something Japanese people are familiar with. Of course people can read 🅱️🅰...
I'm not very familiar with the diffusion process of jujitsu, but the practice to read 術 somewhat like じつ exists(ed) in the traditional Tokyo dialect.
Japanese WP says:
This is a well-known phenomenon: //u// in Eastern dialects is generally unrounded, so a weakened //ju// could be ...
No. ローマ字 (Roman script) is actually an alternative name for ラテン文字 (Latin script), which only refers to A, B, ..., Z. In Japanese, ローマ字 also means transcribing Japanese words using Latin alphabet, but that's an extension of the original meaning.
A, B, C, ...: Latin/Roman script ラテン文字／ローマ(文)字
0, 1, 2, ...: Arabic numeral アラビア数字
I, II, III, ...: Roman numeral ...
Do you know there are several romanization systems, each of which treats long vowels fairly differently? This Wikipedia article is a good starter.
Nihon-shiki/Kunrei-shiki system: gakkô
Hepburn system: gakkō (although there are many variants)
Passport-shiki system: gakko
Wāpuro style: gakkou
If your teacher is using JSL, "gakkoo" is the ...
To my knowledge, there is no term that specifically means "word usually written in kana". In modern standard Japanese, Western-origin loanwords are almost always written in katakana. Particles, adverbs and interjections tend to be written in hiragana. Learning words based only on kanji may not be a good idea because of this.
Pronunciation of じゅ
In Japanese, the "u" vowel /ɯ/ has a centralized allophone [ɨ] (sometimes written [ɯ̈]) when occurring after /z/ and palatalised consonants /Cj/.1 This is 'halfway between' the standard Japanese vowels /i/ and /ɯ/ (and close to the English vowel /ɪ/ in e.g. hit).
Hence じゅ is commonly realized as [d͡ʑɨ] (as opposed to [d͡ʑɯᵝ]). It may be ...
The history of the character's readings
Let's look at the historical and reconstructed pronunciations of 術:
Old Chinese reconstruction:
Middle Chinese reconstruction, the hypothesized source of modern Chinese dialectal readings, and Japanese and Korean borrowed readings:
No romanization systems currently in use today use diacritics on consonants. I think it's non-intuitive to both Japanese and English speakers.
Portuguese-style romaji was used in the 16th century, and it included some diacritics. Historically, there were also French-, Dutch-, and German-style systems (see a table in the middle of this page). I don't know ...