The Rain That Shook The World is Esper Zero's hallmark Neverness to Everness, and at the time of writing, players can only get it by purchasing a premium pack from the game store. The pack in question is called the Limited Press Arc Pack, and you'll also get some extra gacha currency along with The Rain That Shook The World. Thankfully, the package itself is pretty cheap, and if you're not sure if you want to commit to it NTE however, the Limited Press Arc Pack may still be worth getting.

How to Get All Free S-Rank Bows in NTE (S-Rank Weapons)
NTE is pretty F2P friendly in the early game, as you can collect free S-Class Arc for your characters by playing the game.
Where to get the rain that shook the world arc in NTE
You can find this Arc for Esper Zero by go to the Gift Center tab in the Template (microtransactions) in-game menu.. The Limited Press Arc Pack containing the rain that shook the world arc is $2.99 – no need to buy any Rift Crystals and deal with delicious conversion rates either. It's a straight purchase that you can only do once.
Since the Limited Press Arc Pack is a one-time offer, players will not be able to buy it again for more The Rain That Shook The World copiesmeaning you'll be stuck with an M0 version of that Arc for a while. We are not sure if this can be obtained in any other way, but when we know for sure we will update this guide accordingly.
Just to be safe though, pay attention to what Arcs are on offer in the Arc Shop tab. The Rain That Shook The World may be added or rotated there in the future, though it's too early to say for sure.
Is the rain that shook the world worth the money?
For a three dollar package that gives you the absolute best Arc for Esper Zero in NTE, I'd say it's worth buying for anyone who wants to take the game seriously. It's a low-investment option that makes for a very solid character, and you get 180 Riftcrystals from the Limited Press Arc Pack as well. That's a little more than enough for a single gacha pull-in NTE, and if you don't want to spend it on any of the gacha banners, you can always save it for later when something cool shows up in the store.
The rain that shook the world effects
This stat reflects that of a level 80 version of Arc.
The Rain That Shook The World grants its users a 30% bonus Cosmos DMG increase for their redirect and ultimate skills. In addition, it provides a an additional 36 cycle intensity for 15 seconds when the arc's wielder uses a redirection skill. This Arc is practically tailor-made for Esper Zero, as they really use both of their skills as their main sources of damage.
For the unaware, Cycle Intensity affects the damage dealt by Esper Cycle reactions i NTE. The game selects whoever has the highest Cycle Intensity of all characters involved in a reaction, and the damage dealt by the resulting reaction is based on the character's total Cycle Intensity stat. Esper Zero's ability to fully charge their Esper meter after using their redirect skill allows them to keep The Rain That Shook The World's Cycle Intensity buff active throughout the fight.
If you don't want to spend money on this Arc, consider getting the Day Off Arc instead. Alternatively, you can use Fluff of Fearlessness from the battle pass. The latter increases its wearer's ATK stat every time they use their Ultimate, which isn't bad for characters like Esper Zero who rely on their Ultimate for damage.