Oh I assure you that there is nothing illegal about Japan annex Korea, not under the Japanese constitution.
donga.com[English donga]
Scholars Declare 1910 Annexation Treaty Invalid
MAY 11, 2010 07:10
A group of Korean and Japanese scholars said Monday that the treaty that Japan used to annex the Korean Peninsula in 1910 was illegal and invalid.
Commemorating the centennial year of the annexation, a combined 214 intellectuals from Korea and Japan declared a joint statement to that effect at news conferences in Seoul and Tokyo.