Normally, one is intended to be unable to obtain Fireburst before defeating Blight to lift the curse on Sei-an. The restaurant where one gives Yama the Golden Mushroom to learn Fireburst is inside the Cursed Zone in Sei-an Commoner's, and so is inaccessible. However, by performing an Interior Clip, one can enter the restaurant without lifting the curse. Yama is still present, allowing you to obtain Fireburst earlier than intended. This can be used to skip Veil of Mist in the Imperial Palace, or to skip the Imperial Palace (and Sunken Ship) entirely in combination with Fire Tablet Skip.
In NG+ Any% speedruns, Fireburst is skipped entirely. Its only required use would be in Wawku Shrine as an alternative to Inferno, but Wawku is skipped via Ark Early. In NG+ AB, Fireburst Early is performed by KT'ing over the entrance gate immediately after Entering Sei-an Commoner's from Ryoshima Coast. Once over the gate (and careful not to land inside the loading zone back to Ryo), you can just jump off the collision and curve back under the map to reach the interior of the restaurant. This is located, roughly, just North of the icon on the overlay map for the Weapons Shop (between the "scissors" at the top of the icon).
If you don't travel far enough North, it's possible to land on slippery collision just underneath the restaurant, in which case you can just double jump through the restaurant's floor. If you travel too far, you may end up behind the invisible wall which divides the area of the room behind the oven from the area with Yama. You may be able to escape from here via KT's.
Fireburst Early is used in both NG Any%, where it enables both City Checkpoint Skip and Fire Tablet Skip to be used in the same route, as well as NG AB, where it is mainly a convenience to avoid going to the Commoner's Quarter just to obtain Fireburst.
The principles of how it is executed are mostly the same as in NG+, except getting out-of-bounds is more involved.
- Get on top of the wall South East of the item shop. Make sure to start from the portion with higher elevation.
- Tackle, jump, and double jump for height while trying to navigate on top of the collision for the roof of the city gate (to the right).
- At the peak of your jump, air tackle at an angle, such that Ammy bounces off the slope, but not straight back off the slope. If done correctly, Ammy will become grounded at the edge of the slope.
- Before Ammy slips off the slope again, double jump South to gain more distance along the slope.
- Ground tackle, then jump, double jump, and air tackle bounce for height toward South. Keep holding forward (South) until Ammy lands as far up the slope as possible.
- As soon as Ammy lands, ground tackle and double jump again holding South/forward. Don't air tackle this time.
- Again, once Ammy lands, ground tackle. This time, double jump South East (forward/left) to get farther up the arch of the gate. At the peak, air tackle bounce and hold South to land on the very slippery slope.
- Note: If you go too far left, Ammy will just slip off the arch without becoming grounded. This is because Ammy that part of the arch is higher up. Ammy needs a certain amount of falling speed to land on very slippery slopes, meaning she will not land on slopes just below the apex of her jump. The idea here is to go as far left as you can (gaining as much height as possible in one step), without just slipping off. This takes some practice to get the right feel for.
- Repeat, moving further left, until one is past the invisible wall at the top of the arch.
- If done optimally, this should only take a single air tackle bounce on top of the arch.
- Air tackle past the invisible wall, then hold West/right to avoid landing inside the loading zone.
- Land on the out-of-bounds collision behind the city gate. From there, tackle-jump off the collision and curve back around under the map to reach the restaurant interior, as described above.