[@anothered]

1. The Kikai clan started out as a nameless bottom feeder clan prior to the Village era until a medic ninja named Baraba started doing some experimentation to deal with the crippling injuries and lost limbs that were hindering the clan. Through trial, error, experimentation and almost certainly some crimes that the clan keeps very quiet, Baraba developed the secret of living metal and fusing machinery and flesh together.

2. This discovery altered the clan heavily from scavengers that were barely surviving to a major clan in the region. Mechanically speaking, the Kikai who opted to undergo the process of being augmented were trading raw chakra and finer chakra control (ie, the ability to use Ninjutsu and Genjutsu) for vastly improved Taijutsu and near immunity to Genjutsu (because of reasons listed in the above clan history). To make up the difference for the loss of ninjutsu, weapons and tricks were installed into their bodies in a manner similar to puppeteers. 

3. Rather then compete with the Senju and the Aburame, both of whom the Kikai were weak against, they instead joined them in an alliance against the Uchiha, with the Kikai and Aburame filling in the Senju ranks where their strongest members couldn't be during larger conflicts. 

4. When Konoha was formed, the Kikai were invited and they joined. 

5. During the third war when Konoha was being pushed back on several fronts, a sub-sect of the Kikai developed chakra powered war engines of highly destructive power to help turn the tide without sharing with the rest of the clan how they did it. When they were investigated, it was revealed that this sub-sect had developed a method of randomly summoning summon creatures without the need for a contract, which they would then forcefully and painfully bind to their war engines to serve as fuel. Horrified by these actions and with fear that Konoha would come down on the whole clan hard if they didn't act (since Konoha had a number of summoners, including the Hokage themself) they tried to end the practice and bring those accountable to justice.

The sub-sect violently disagreed with the rest of the clan, activating and turning their remaining war engines on them in the process. Many Kikai died and the destruction and bloodshed spilled out into Konoha proper. The traitorous sub-sect fled the village in the chaos, with the Kikai loyal to Konoha instead focused on trying to stop the carnage rather then pursuit. Their heroics and the amount of Kikai that died in the incident somewhat shielded them from the legal consequences of the whole mess, but even years later the incident lingers in the minds of many. 

6. The traitorous sub-sect still exists as a rogue ninja faction, creating and refining their weapons of war and selling them to the highest bidder.