How to write long sound to emphasize words?

Question

For example, I want to emphasize the word しらない by saying shiiiiiranai, しいいいらない seems a little bit weird to me. How do you write this in japanese character, can we also write this in the form of kanji?

Answer 1

Yes, writing it as しいいいらない is okay, but is relatively uncommon. More common ways to write this are:

• しーらない！
• しーーーらない！
• し～らない！
• し～～～らない！
• しいぃぃらない！ (with small ぃ)

Needless to say, don't use these in business settings or in formal letters.

See Also: ー vs small kana vs long kana for writing long vowels

Answer 2

全然知らない。I don't know at all.

しーらない、知らないもんね is like female or child. It means "so I am concerned about that."