This is the fastest event we've had, only a few weeks apart. For story enthusiasts (myself included), this is great as it means the hype is still running strong but those that are avid Shikigami collectors, there's just not enough time to accrue jade or amulets for a chance at summoning the newest SSR, Asura. Not without paying and extreme luck on the side.
There are 4 chapters/areas in total: Hell of Fire, Hell of Ice, Hell of Pain and city of Zenken. You will spend 3 days in each area. Every day a new story chapter will be unlocked.
Sanity is required to battle in the abyss and Monster Bone is the currency used to purchase items. You can claim extra Sanity from [Tanuki's Wine] every day after 6:00 and 12:00 and it resets after 24:00.
There are 3 ways to participate in each area: Battle, Dispatch or Donate. The status of each area can be revealed by clicking on the Eye icon (Asura's vision). Each attempt costs 15 Sanity. Be very careful with Dispatch as each slot costs 15 Sanity and you can easily burn through your supply if you're not careful.
Goal: Activate the Tower of Sins (Passive currency), complete all 3 Wanted quests and supply Asura's Stamina by feeding him Devil Peppers.
Quest include Main, Quests and Wanted.
The Main Quests are Server Goals, meaning the entire server works toward this goal. You are not expected to solo.
Quests are Archived Quests, meaning they accumulate based on participation.
For example: Donate a total of 5 Devil Peppers. Rewards include: Monster Bone, Exclusive frame for the Return of the Mara event, Sanity and Devil Peppers.
Wanted Quests: You get 3 Wanted Quests daily. Completing all 3 will grant you 6 Devil Peppers. Feed Asura the Devil Peppers by clicking on the +Devil Pepper icon hanging over his head.
Spiritual Entity is where you equip skills for your team. You will need Spiritual Entity Shards (found in certain areas) in order to unlock slots (a total of 6) to equip skills. Select Equipped to begin equipping skills.
Illuminated Fragments: A fragment is unlocked every time 5 Spiritual Entity Shards are collected.
Hell's Dirge: The progression of the event's story. A new piece unlocks daily.
Reunion Moments: CG Animation can be found here.
The Abyss Vault is this event's shop and notable items are dependant on the player's level and currency.
My typical approach for events (if the interest is high enough) are wallpapers, special skins, Mystery Amulets, Skill Daruma or shards, Realm Cards, Frame and the SSR/SP Summon Scroll if I can get it.