EDIT: Looking back, I see the crew has used the user vote as a manner of deciding upon system updates in the past, I'll apply the same system here given the crew's lack of activity at the moment and the urgency of updating these parts of the system.
Blocking
Basically, this makes blocking more simple and a more relevant and balanced part of the combat system. The formula is changed so that the block formula is more on par with the attack formula than it is now.
Covering and Rescuing
For rescuing and covering, this modification is VERY needed since, as the system stands now, one guy with high dodge rating in a group of twenty people could single handedly prevent all of them from being hit by 30 attackers since the action of pushing a friendly target out of the way does not use up attack turns.
Since taking damage and moving someone out of the way now requires that you are actually in a position to provide cover for someone now makes more sense and balances out this action. I made covering and jumping to the rescue separate techniques since, even though the basic principle is similar, one should be much more difficult to execute than the other and should have less chances of succeeding.
Grappling
This is also a problem I've been meaning to tackle for a while now since, as the system stands right now, I don't see why a taijutsu user would do anything but grapple all the time since it is exactly the same formula as any attack and causes just as much damage. I understands there could be chokeholds and submission techniques but, in my mind, these should be individual techniques themselves.
I also made two different ways of breaking free of a grapple, either by slipping away (escape artist) or powering through (athletics). For the moment we have a break grapple technique that would maintain its relevance if grapple is now made like this.
Anyone would have a better image for the grapple by the way?
I came up with these pretty quickly so don't hesitate to mention if there's anything you'd add, remove or modify in this proposal.
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Uke (Blocking)

Blocking is the most basic defensive maneuver a shinobi can learn. Aimed at preventing an attack from reaching its target, a block is basically a blow against a blow, applying the basic principle that two equal forces going in opposite directions will offset each other. Unless very specific skills have been learned, hands will not prove very helpful in blocking weapon attacks.
Attack Turns: 1 (Reaction)
Cp Cost: n/a
Damage: n/a
Requirements: Learn in the academy.
Training: 1 stage
Stage I: Weapon or Taijutsu DC 10, Deflect attacks with your own to prevent them from hitting you.
Special:
*Roll 1d20 + [Base Attack Bonus / 2] + Strength Modifier + 2 per 10 in Weapon Skill. If block check beats the attack roll, the attack was succesfully blocked and causes no damage. If failed, blocker takes full attack damage.
*Bare hands can only be used to deflect taijutsu attacks.
Kabaiitate (Cover)

The action of covering someone is made to protect more vulnerable targets in order to prevent that harm be done to them. Any person wishing to attack the protected target will have to “go through” the person covering them, something that can be quite a challenge depending on who they have to deal with.
Attack Turns: 1 per action (reaction)
Cp Cost: n/a
Damage: n/a
Requirements: Learn in the academy.
Training: 1 stage
Stage I: Weapon or Taijutsu DC 10, Prevent attackers from damaging a target placed behind you.
Special:
*The action of moving to cover someone or moving into cover requires one attack turn to perform.
*Protector can use cover actions while providing cover.
*As a cover action, user can block or defend attacks aimed at the person behind them as though they were aimed at them.
*As a cover action, if protector’s dodge or reflex beats incoming attack score, they can take damage for the protected person.
*As a cover action, if protector’s dodge or reflex beats incoming attack by 10, they can move the protected person out of the way and dodge the attack themselves.
*Cover is broken as soon as an offensive maneuver that requires that the protector move from his spot is initiated (melee attacks, any jutsu requiring movement).
*Only 1 person may be covered at a time, although many people may provde cover for a single individual.
Kanshou (Intervention)

If an attack is launched against a target that a shinobi wishes to protect, they can try to wedge themselves between the attacker and its target either to attempt to block the attack, take damage for them or to push them clear out of its way.
Attack Turns: 1 per action (reaction)
Cp Cost: n/a
Damage: n/a
Requirements: Learn in the academy.
Training: 1 stage
Stage I: Dexterity DC 10, Wait for the signal and push a training dummy out of the way of a swinging log before it takes any damage.
Special:
*If protector’s dodge or reflex beats incoming attack by 10, they can take damage for the protected person.
*If protector’s dodge or reflex beats incoming attack by 15, they can attempt to block or defend from the attack.
*If protector’s dodge or reflex beats incoming attack by 20, they can move the protected person out of the way and dodge the attack themselves.
*After an intervention attempt, successful or not, target will be put under the user’s cover until it is broken.
Kumiuchi (Grappling)

Grabbing an opponent in combat is a basic taijutsu technique aimed at holding an opponent in place rather than causing to damage to them directly. Getting close to an opponent, the person intending to restrain the other must find a way to get his hands on them and lock them in place to prevent any movement. This allows the victim to be used as a human shield or facilitates any partner's attempts at attacking them. In order for the victim to break free, they must either find a way to wiggle free from the user's hold or overpower them to break it.
Attack Turns: 1
Cp Cost: n/a
Damage: n/a
Escape Artist DC: d20 + Strength Modifier + 2 per 10 in Taijutsu
Requirements: Learn in the academy.
Training: 1 stage
Stage I: Taijutsu DC 10, Hold a struggling target in place while they are greased up, it can be quite a challenge!
Special:
*Grapple is initiated like any other melee attack but does not cause damage.
*Immediately following a succesful grapple attack and at the beginning of any round that the hold is maintained, user and defender must roll a Grapple check of d20 + Strength Modifier + 2 per 10 in Taijutsu to see if the grapple is maintained or broken (higher score wins).
*While grappled, victim rolls a free grapple check (d20 + Strength Modifier + 2 per 10 in Taijutsu) per round against the grappler's grapple check to attempt to break free from the hold, and may use their attack turns to attempt Escape Artist checks against the Grapple check to break free.
*While grappling or grappled, victim and grappler lose the benefit of their Dexterity to their dodge rating and may not attack other people, block, or use techniques that require more than 1 attack turn (dice roll).
*While grappling, grappler can use attack turns to either attempt taijutsu or small weapon attacks against the grappled target, attempt to disarm them, or attempt to wrestle them to the ground, negating their wisdom modifier to their dodge rating until they break free or until the grappler attempts another grapple action.
*While grappled, defender may attempt taijutsu attacks against the grappler but suffers a [4 + 1 per 10 in grappler's taijutsu skill] penalty to attack score.
*Any failed attack against the grappler or the grappled target has a 50% chance to hit the other party to the grapple.
Imashimeru (Binding)

Using rope to immobilize and restrain an opponent is a basic maneuver often used by shinobi for various purposes.
Attack Turns: 1
Cp Cost: n/a
Damage: n/a
Escape Artist DC: d20 + Sleight of Hand + Str Mod
Requirements: Learn in the academy.
Training: 1 stage
Stage I: Sleight of Hand DC 10, Tie up one of your buddies as tightly as possible and see how long it takes for them to break free (often trained in conjunction with the Rope Escape Technique).
Special:
*Can only be used against an immobilized or grappled opponents.
*User must use this technique for (5 - 1 per 15 in Sleight of Hand) continuous attack turns to succesfully rope up an opponent.
Youdou (Feint)

A combat application of masking your true intention, a shinobi can perform a feint in combat intended to mislead an opponent. The user fakes an attack in one direction to force a reaction from the opponent by telegraphing false information through body language and then uses the confusion to strike from another direction. If done successfully, this technique can leave an opponent wide open for an attack, greatly reducing chances of dodging. One of the weaknesses of this technique comes form its dependance on the opponent's ability to read the user's movements, making it less effective against targets that have different body types or limited intelligence.
Attack Turns: 1
Cp Cost: n/a
Damage: n/a
Sense Motive DC: d20 + Innuendo + Charisma Modifier
Requirements: Learn in the academy
Training: 1 stage
Stage I: Taijutsu DC 10, Spar with an opponent and bait him to move in the wrong direction in an attempt to dodge a false attack.
Special:
*Roll an Innuendo check (1d20 + Innuendo + Charisma Modifier) against an opponent's Sense Motive check (1d20 + Sense Motive + Wisdom Modifier). If Innuendo check beats enemie's sense motive check, user's next melee attack that only requires one attack turn is considered a sneak attack and gains all bonuses accordingly.
*-4 penalty to Innuendo check against non humanoid creatures. -8 penalty against creatures of animal intelligence. Impossible against creatures devoid of intelligence.