"ciaossu" means "ciao" from italy and "ossu" from japan,

Its a way to say hi

From the Manga and Anime. Katekyo Hitman Reborn!
Ciaossu. Have you been taking good care of Tsuna around here? ...
by Gokudera July 13, 2008
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Ciaossu mean "chaos". But in Japanes they say "Kaossu" (or something like that) Reborn use "Ciaossu" because he is kid and he does not pronounce correctly. "Chaos" is Adult Reborn saying.
Ciaossu. Have you been taking good care of Tsuna around here? ...
by Tsuna-Kun June 22, 2019
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