(informal) Used to sign off a message/attribute a text.

A glottal stop or “choked sound”. / The sokuon: a small form of ツ (tsu). In romanization, this is represented by doubling the following consonant. The equivalent in hiragana is っ.

The long-vowel mark, which marks a long vowel in katakana (and less commonly in hiragana) when placed after a syllable.