*I start by performing the required hand signs Snake → Ram → Monkey → Boar → Horse → Tiger, as I'm doing this I gather a large amount of katon chakra into my lungs. Once I've gathered enough I then use my thumb and index finger to create a ring, and I blow outwards expelling a large fireball that is created as soon as I blow through the ring. The fireball hit a nearby tree and sets it ablaze.*
Pros: Decent damage projectile technique that has a fairly good area of effect as suggested in the description along with low chakra cost.
Cons: Requires a poop load of hand signs to perform which will increase the prep time to execute the technique. Short range of 0 to 5 meters only as well.
This technique is performed by weaving the required hand seals and after gathering a large portion of katon chakra, the user must form a ring shape with their thumb and index finger before expelling.
This technique does good enough damage to burn the opponent pretty badly, so I'd say that given that it's a projectile based technique, the best way to use it would be to ensnare the enemy, hindering their movement or by trapping them within a confined space.
This technique can be defended against fairly easily due to the fact that it's a projectile based technique. Although it has a large area of effect the user's enemy may simply put up a B rank earth technique or any other higher ranking jutsu to encase/protect themselves from the blast.
It's effects, if making direct contact it will severely burn the target hindering their movement if a limb is burned badly enough. The limb might also become numb due to the burn.
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*I begin by pulling out a lighter, proceeding to spark a flame with one pull of the thumb, and toss it about a meter away from directly in front of me. By manipulating the flame with my katon chakra I then proceed to turn the flame into a wall of fire. The wall of fire is large enough to protect me from incoming small objects.*
This is a weird technique. (O_O)
Pros: No hand seals required so hardly any prep time at all. Great means for defense, and a good way to get the opponent to back off. Burns small incoming projectiles as well.
Cons: Well.. if one does not have a lighter than the user could not execute this technique, unless you stated that you had a lighter in your pouch in the beginning of a battle. Or is it like kunai and shuriken where it's basically a given that you'd have a lighter in your pouch? Anyways. xd It can only protect against
small projectiles.
This technique is executed by tossing a lighter and utilizing shape manipulation to turn the flame into a wall of fire.
It's effects are that it can burn up small incoming projectiles which may come in handy when being bombarded with them.
As said above if the enemy is launching multiple shuriken at you and uses the shuriken shadow clone jutsu, then this technique would be perfect to defend against them.
Seeing as to how this technique is not an attack or an offensive move but rather a defensive one, I do not think their is any way to "defend" against it.

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*I turn towards a nearby tree and make the Tiger hand seal. I then gather a sufficient amount of my katon chakra and proceed to create a stream of fire, using shape manipulation to then turn the stream into several rings of fire that run along the ground towards the tree. Upon contact the tree is set on fire and burned down.*
Pros: Has a good range of 0-10 meters. Does good damage and can be manipulated several ways before reaching it's target.
Question: Regarding the manipulation part, is the user only limited to change it to "(rings of fire that runs on the ground or a circle of fire flying through the air)" Or can they get creative with it?
Cons: Requires one hand seal to create increasing prep time.
This technique is executed by striking the Tiger hand seal, gathering katon chakra and releasing it into a stream of fire that can be manipulated.
It's effects on the opponent might slightly vary on how it's manipulated, however the result might be the same, burns across the contact area that may hinder the opponent.
This technique may best be used when the user has a clear visual on the opponent and when they are in range, if the opponent sends a lower ranking technique at the user then this attack may overpower it.
Best way to defend against this technique would be to encase yourself within something strong that could withstand the full force of the jutsu.