One of the most famous bits of Pacific Rim, and one of the most mocked. "Why didn't they use the sword earlier?", you ask? "Why didn't they use swords on all Jaegers?", and so on. Well, there are answers to all those questions and more.
So why didn't they deploy the sword earlier? Because it wasn't originally part of Gipsy Danger. It was added when it was being repaired. Mako knew about it, but didn't transmit the information across the drift to Raleigh because she was avoiding trying to think about unnecessary things.
Unnecessary? Isn't the sword a super weapon?
Kaiju blood is poisonous. So what'll happen if you start chopping up a kaiju in the middle of Hong Kong with the sword, spilling its blood everywhere? Well, they'd git rid of the kaiju...and turn Hong Kong into a toxic wasteland.
In fact, this is a major reason they use giant robots in the first place. You can blast fire a kaiju with hordes of artillery and missiles, sure, but it's going to charge through the storm through the city where it finally explodes into gibs, again spilling its blood everywhere.
The Jaegers, however, can physically restrain kaiju, keeping them away from cities, and use blunt force to inflict damage without spilling blood.
In fact, every weapon a Jaeger uses is made to not spill blood. Gipsy Danger uses plasma weapons to cauterize wounds as they are inflicted. Cherno Alpha has flamethrowers and electrically charged fists. Even Striker Eureka's missiles are designed to explode in ways to cauterize wounds.
And when Jaegers do have cutting weapons, they have extra stuff to fix blood spills. Crimson Typhoon has a plasma weapon that it can use to cauterize its slices. Gispy Danger does the same, though it got the sword later, and never put into practice due to the events of the film. Striker Eureka's swords are heated, burning wounds closed.
This logic extends all the way back -- Tacit Ronin, one of the Jaegers we see in the opening news reel scenes, is primarily sword based...but it's also paired with Coyote Tango, which uses ranged weapons and can cauterize the wounds inflicted by Tacit. (Incidentally, Coyote is Japanese, and Tacit is American -- but given that they're paired, the idea was that they would give the Jaeger's a name based on the partner Jaeger's culture. Explaining why Coyote Tango has such a name despite being Japanese.)
So, Pacific Rim is a dumb movie, right?