The Ikaruga Tuna (イカルガ鮪 Ikaruga Maguro), also known as the Crimson Grimoire (紅の魔道書 Aka no Madōsho), is a large, tasty fish that can be found in the River Styx. It is featured in Ragna the Bloodedge's gag scenario in BlazBlue: Continuum Shift.
The Great Dark War wiped out most species due to the spread of Magic Element and, as such, tuna is now rare in the world of BlazBlue. This tuna, however, seems to be so good that Rachel and Nu trade Ragna for it. It also causes the logical Tager to want it, even though he does not eat and he usually would question these actions constantly as he does in his gag scenario.