when did he lose his arm? I forgot :)

i think it was on the closed island thing where they were ambushed, that's where he met duke too.

Not ambushed. It is from the battle between top 10 of the world academy and the frame kids. It is acknowledged so it definitely was not an ambushed.

Yea, the kids from both places had a match after Frame attacked the world awakener academy. To like "ease tensions" or something.