Regain possession of Yamato!
This mission throws you straight into the action. First of all dash through the first mining area as there is nothing here bar a few red orbs in the lower section. This will lead to the port. In this area alone there are some scarecrows, followed by biancos and altos. Kill them all to unseal the area then make for the residential district.
Use wall kick to claim the hidden red orb stash on top of the metal tower before going uo the stairs. This area is full of assaults and then mephistos and finally a faust. This area is narrow so do not get cornered by the assaults or let the mephistos sit around outside the walls or this section becomes a lot harder than it really is. Smash the red orb cluster after defeating all of the demons and break all the jars and boxes at the end for a few extra orbs.
There are three mega scarecrows and a large number of little ones immediatly in this area. Killing these will summon in some basilisks. These enemies are not too tough but there are lots of them so watch out. Smash all of the benches and trash cans that line the streets for red orbs and grab the blue orb fragment before moving on.
Opera House Plaza
At the beginning of this area is the final secret mission, hidden behind a trash can. Go through the archway to be confronted by a pair of altos and then a pair of fausts. It is possible to enter the warehouse area for a few extra orbs but it takes time so avoid if possible. Take the huge green orb outside the door and use the divinity statue if needed.
Boss Fight: Alto Agnus
Like every other boss Dante has fought thus far, Agnus has hardly changed at all. In addition to his health sapping attacks, fireballs and the ability to summon gladius swords and cutlesses he can now summon basilisks as well. Use the white orbs obtained from defeating his cohorts of demons to power long devil trigger attacks against him and he will die eventually. Go down the lift to reclaim the Yamato sword which gifts Dante the Dark Slayer style.