(Part 1 snake form)
This form is the same form you see him as in Onimusha 1 deffently brings back memories. luckliy for you youre in youre ultra powerful onimusha form. Youll basicly being flying around trying to avoid fortinbras attacks. He can damage you very quickly but the best thing to do is make sure youve got plenty of oni magic and keep striking him with the oni magic strike which will do massive damage each time. Other than that he is very hard to damage youll probably die before you can kill him. So the key to beating this form is the oni magaic strike. Using this teqnique makes this form rather easy but this is only prequal of the battle ahead which is one of the most challenging and annoying battles you will probably ever face only phanlax is tougher.
(Part 2 Final Battle Human Form)
For the final battle youll find youreself in a ground based arena youll only be in youre normal form. Fortinbras will now be in he's human form. Don't try and attack him as at the moment he can't be hit. Ok now what you have to do is dodge all of he's attacks. When he shouts i am the god of light watch out for he's mutiple laser teqnique just run the hell away if it hits youre in for serious damage i would advice using a super oni magic strike to avoid further damage if hit as it doesnt stop for aqhile this wayyou will avoid bigger damage. Ok then wait for him to charge up he's attack. Start to absorb the souls from he's attack which will weaken it. He will then fire a red ball at you which is he's ultimate attack if it's big run out of the way but if it's small then youve absorbed enough souls. Hit the ball back with a normal strike and it will hit him blinding him for a short time. Then the annoying balls floating around which were invincible must be destroyed before Fortnbras recovers. Get them all and then Fortinbras will float down giving you a chance to hit him and finally land some damage. If you transform into youre onimusha form you can land alot of much bigger damage use the oni magic strike that is the most effective. But with normal strikes the damage is less but normal attacks will be 50% - 70% of what youll probably hit him with. repeat the process intil half he's life as gone and then things get even harder. All of a sudden these little annoying green orbs start to appear which shoot lasers try and destroy as many as you can whilst evading their attacks and fortinbras. If you don't then when Fortinbras charges he's attacks they stop you from absorbing it'spower away therfore making it unblockable so get rid of those. Repeat this and try and survive and you should eventually somehow destroy Fortinbras. After a long hard battle you if victorious can class youreself as a fully pledeged demon hunter. Before entering this battle make sure you bought the most oap/onimusha medacine, tons of health items, and a maxed up sword. I also had the rosamary of peace which restores youre oap gaurge. That helped out alot and finally make sure you have alot of attack boosting items equipped.