Hi Smitha,
You can tell the SQL Server to use any of the n-text types like nchar, nvarchar or ntext. This store text as unicode. Then you can simply store whatever text you receive directly into the table.
If the SQL server is limited to 8-bit or 7-bit text you need to convert the japanese text to a byte array and from that into a string with the encoding used in the database.
You would need to set some flag or put some kind of marker on that text to know when the text is originally japanese and encode it back to its original encoding.
string unicode = "some japanese text";
byte[] data = Encoding.Unicode.GetBytes(unicode);
string newstring = Encoding.Default.GetString(data, 0, data.Length);
Store newstring in the database.