Kikoku is a Relic weapon.
There are 5 items that share this name:
Please follow the above links for more information about the item. Kikoku can be upgraded via Weapon Trials.
Kikoku is Japanese for "Demon Cry" or "Demon Wail". It's derived from 鬼哭, the first kanji being 'oni' (ogre or demon), and 'KOKU' (wail, cry, weep, etc). The 'ON' reading for 'oni' is KI, which is where KIKOKU is made. It was also a Japanese movie from 2004.
There is a misconception among some that the meaning of 'Kikoku' is Japanese for "Return to one's homeland"; this is derived from an actual word, and it is correct (shown in the kanji 帰国 , meaning 'return country' respectively). However, this isn't the kanji the relic katana uses.