Shikigami Weapon - from Pergatory's post on KI
Time of Death
This is the hardest part. Shikigami respawns 21:00 - 21:15 after his last death. For example, if he is killed at 5:30, then he will respawn on the next day between 2:30-2:45. If there is server maintenance, his window will open 21:00 after the maintenance.
The best way to find his ToD is to wait until a server maintenance and then keep an eye on Ro'Maeve. If you can't be online during his window, just assume his window moved backward about 2:40 per day. I found this method to be fairly accurate and I could predict his window a week or more out.
Camping Shikigami
Shikigami is a very unique NM. He pops in a medium-sized area, and runs around in that area at Flee speed so he's hard to keep up with. In addition, he's totally invisible and untargetable until aggro'd. He only aggro's magic, and he does not link. So the method for claim is that you must aggro him by casting near him, then someone must claim him. See the image below, the area highlighted in blue is Shikigami's playground.
The areas circled in red are relatively safe camps, with usually only 1 or 2 mobs within magic aggro range. Good bases of operations while you wait for Shikigami to pop.
When camping Shikigami, you absolutely MUST have a widescanner. Most widescanners should be able to see the entire area without any problems so 1 is enough. When the spawn window opens, the widescanner should spam widescan over and over. Shikigami will always appear at the bottom of the list if you are spamming widescan, so just go straight to the bottom. When the widescanner finds Shikigami, he should immediately announce to the group that Shiki is up, and tell them where he is or lead the group to him. Remember that he has constant Flee, so communication is important between your widescanner and your casters.
Tip: This is the part where I was able to gain my advantage over most other campers, because I took this part of the camping very seriously. As soon as the widescanner found Shiki, he would tell us whether it was on the North or South track (see image above), and whether it was on the East or West side of the map. Shorthand, NE, NW, SE, SW, just make sure the people camping know that SE doesn't mean Southeast, it means south track east side. Or you could say top track, bottom track, left side, right side. Generally use whatever is easiest for the widescanner so he can focus on other things. The important thing is to plot out easy & fast ways to verbally identify which area Shiki is in before the window opens so that everyone understands what to expect.
This gave us a very quick method to communicate to all the campers Shiki's approximate location, so that they don't have to depend on following around the widescanner until he says "here". It also allowed us to spread out and cover the whole area even with only 1 widescanner. Since he runs so fast, it's important for the widescanner to continue providing heading information to the group until Shikigami is claimed, for example, "still heading east" or "moving to north track".
Claiming Shikigami
Anyway, once the group has an idea of where Shikigami is, a caster should run in front, and the claimers should follow. Make sure that all your claimers don't just run off ahead of the group!! They are totally useless by themselves. They should be next to or behind the casters. When you get to the area you believe Shiki to be at, a caster should cast a spell like Sneak or Stoneskin to aggro the area. If you did correctly, Shikigami should reveal himself (he will still be unclaimed) and will attack the caster. This is when the claimers need to step in and claim him ASAP!!
Don't worry too much about adds, they are pretty easy to sleep. Make sure your main tank gets hate on Shikigami ONLY, and not any other mobs, in case things go wrong with the adds. Shikigami himself isn't too tough, two or three people should be able to take him out but the adds complicate matters considerably.
Tip: I was able to claim Shiki several times by having Carbuncle out when I cast. Just this last time when I got my robe, it was only me & a NIN nearby, the rest of our group was all the way on the other side of the playground. However, the widescanner relayed Shiki's position to us, and so I was able to get to him and cast Stoneskin on myself. I aggro'd about 5 different things, but one of them was Shiki and Carbuncle immediately auto-attacked him due to him aggro'ing me, claiming him in the process before anyone else around could even target him. My NIN then voked Shiki away while I died from the aggro. The NIN was able to keep Shiki occupied while the rest of my group got there, so even though it got me killed, I secured the claim by myself using Carbuncle. I don't know if Carby will always pick Shiki if you get multiple aggro's from your cast, or if I just got lucky. As a caster, you have to be willing to die if you expect to be competitive at claiming this NM. I've seen people simply running down the hallways casting and training rediculous numbers of weapons. It's a crude way of doing it, but it works.