Help me design a flavorful prestige class!

I had a great idea to create a five level prestige class where two people have a Supernatural bond enabling to fight together more efficiently. The characters getting this class will be two dwarven fighters, so it will be a melee based class. Here's what I've got so far.

Preqs - Shield Wall Tactics, Improved Shield Wall Tactics (what book are these from)

BAB - Full, Saves - Fort good

Bond (Su): Upon gaining their first level of _____ a _____ must select one person. All _____ abilities only work when this person is alive and both are within 100 feet + 10 feet/level. (Should this partner have to have a level of the PrC as well?)

Simultaneous Reaction (Su or Ex?): At first level a ______ gains the ability to share initiative checks with their partner. Both characters use the higher initiative check.

Improved Aid (Ex): At Xth level the _____'s Aid Another actions become more effective. At Xth level the bonus increases to +4, and at Yth level the bonus increases to +6, and finally to +8 at 5th level.

Improved Flanking (Ex): At Xth level the _____'s gains the ability to flank opponents more effectively, but only when the other flanker is the partner. The ____ gains an additional +2 to attack. At Yth level, the _____ adds +2 to damage, and at 5th level the bonus increases to +4 attack, +4 damage.

_____________ (Su): At 5th level the _____ gains the supernatural ability to pass through his partner, enabling them to fight in the same square effectively.

Help me fill in the variable levels, the blank ability and class name, come up with other flavorful abilities, and anything else you can do.

You might like the Harm's Way ability from the Bodyguard advanced class (from d20 modern).

Once per round, if the Bodyguard is adjacent to an ally who is targeted by a direct melee or ranged attack (but not an area effect), the Bodyguard can subject him or herself to the attack in the ally's stead. If the attack hits the Bodyguard, he or her takes damage normally. If it misses, it also misses the ally.

Swap "ally" for "partner" or whatever the two dwarves call each other.

For "Bond", yes, the partner should have to have a level of the prestige class, too. Call it "pair fighting", and note that dwarves have long used this technique, fighting back to back in the tunnels of their homeland. If one dies, the other typically goes on a last rampage down into the orc-held lands, never to return.