How exactly can we get Odin Gear?

[Kaworu]

The gear that's in separate pieces for left side comes from the Odin trial. I imagine it must take a long time to get the entire set because I've never gotten this in trial roulette and I hear some parties have trouble downing him. Also, the gear is separate between DoW and DoM, so you'd not only have to see the specific item you want drop, you'd have to then win the roll on Need against other eligible party members.

The other gear requiring 5 mantles is only equippable by tanks, but you can see it in Mod Dhona.

Is it hard to get those mantles?

[ChiiSoSeriouz]

Is it hard to get those mantles?

It can be, due to the sporadic nature of the fate pop. You can get 5 Odin's Mantles by completing the Odin FATE entitled "Steel Reign" with a gold rating. But when the fate pops is random and about once a week approximately.

The only way to know when it's available is to pay attention to the weather in The Black Shroud. Odin has his own rare weather event, which is very hard to miss. All zones in the shroud (with the exception of Gridania) will turn dark and dreary, with what looks like ash floating around. I've seen this weather labeled Hopelessness or Tension. Be advised this weather change will only happen at night (Eorzea Time).