'Chapter' One of Isomer is divided into three Paths, labeled A, B, and C. The A Path is the top of the side scrolling layout. B is the central line, and C is the bottom. Each ‘Path’ features two Combat Stages and a selection of story stages. There is also a short introductory stage. Story wise, Isomer picks up immediately after Chapter 11, following several different threads.
Isomer is a bit of an oddity of an event, frontloading a lot of its difficulty, both in Normal and Ex Mode. Normal throws relatively heavily armored KCCO units into the fray, as well as some lightly shielded Pardeus enemies, and one very scary, but avoidable Boss.
EX meanwhile, pulls out all the stops, with a large variety of heavily Armored KCCO units, Typhon tanks, Hydra and more. Shielded Doppelsolders and Uhalns also feature on several maps, with HOCS also needed to destroy Emplacements.
The following teams are EXAMPLES only. They should be taken only as guidelines, not as hard and past rules for what you should use to complete these stages. Use your best equips possible in all cases. As a rule, aim for greater synergy than I have on some of these teams, especially the low-level RF squad. If your HGs are struggling to survive on Normal, try swapping the main tank for an SMG to gain some durability.
Normal Maps will need at least level 30 3x linked Dolls by the end, although at the start you can make do with weaker Echelons.
EX Mode does not play around. You will need to bring at level 90 5x Linked Echelons with good equipment, the best fairies you have (fairy requirements aren't that high, as you can see), and you will want a level 60 BGM (additional HOCs optional). The requirements for EX are the same across all chapters.