On the terrasse's floor should be a fairly wide assortment of weapons. Most Uniques had a plasma rifle, a submachinegun - you're liable to find a amix of these and this ought to only require moving to a body and bending down to pick a weapon of your choice. They're probably already expended to some capacity due to them being used against Kotori before. Each defeated Unique is also liable to carry at least one spare magazine/battery to reload, along with a combat knife. Furthermore, at least half of them ought to have some form of anti-personnel grenades... they were especially outfitted to fight Kotori so they had stronger fare than the ones you fared before - some may have one or two of: fragmentation or incendiary.
Mind, all of those weapons are anti-personnel fare. While they can be expected to hurt the Umbral, the damage will be much more limited than it was with your Daisy plasma rifles. Plasma and fire, of course, will smart more because it'll hinder any self-healing on the part of the Umbral. Most of these will prove lethal of smaller spawns of the Umbral (i.e.: the bugs) though accuracy may become an issue.