For instance, this story is good, but the traits gives too many bad things. I need to give him an advantage.

<defName>RockChildClodfish04</defName>
<title>Servitor</title>
<titleShort>Servitor</titleShort>
<baseDescription>The core tenant of Rockman culture is strength and NAME didn’t have it. Trial after trial after trial saw NAME on HIS knees and with the disapproving eyes of those NAME craved respect from burning into HIM. Disgusted by HIS weakness NAME’s society turned NAME into something other than a rockman so they weren’t related to HIM and HIS weakness, a servitor. One night as NAME was sound in bed HE was pulled kicking and screaming into a Smooth Stone temple. On the alter the Clergy castrated HIM and chipped away at HIS rock skin, HIS very rockmanhood, save for a spot on his helm. There they Carved one symbol, the only one HE will ever have. The carving of a slave.</baseDescription>

-6 melee, -2 construction, -2 mining, forced trait: wimp and nervous

<defName>EngiSlavePerson</defName>
<title>Mantis Slave</title>
<titleShort>Slave</titleShort>
<baseDescription>NAME was a simple engineer, working on starship waste disposal systems. One day, NAME's home planet was attacked by Mantis slavers and NAME was captured. NAME spent years serving the Mantis, until eventually NAME found an abandoned escape pod and managed to sneak on board and jettison it. NAME's time as a slave to the violent mantis made NAME fear any sort of violence.</baseDescription>
<slot>Adulthood</slot>

Not sure which Categories there are.

I think it would give +6 construction,

Forced Traits: None.

Work disables: Violent

It looks a bit like this :
<AlienRace.BackstoryDef>
<defName>EngieAdultClodfish02</defName>
<title>Mantis slave</title>
<titleShort>Mantis slave</titleShort>
<baseDescription>During a transit between worlds [PAWN_nameDef] ship was boarded by a Mantis war party and [PAWN_pronoun] was enslaved to be their mechanic. After numerous beatings and torture all [PAWN_nameDef] will to fight was broken. [PAWN_pronoun] became skilled at fixing mantis ships and begging for [PAWN_possessive] life. </baseDescription>
<slot>Adulthood</slot>

<bodyTypeGlobal>Thin</bodyTypeGlobal>
<bodyTypeMale>Thin</bodyTypeMale>
<bodyTypeFemale>Female</bodyTypeFemale>

<spawnCategories>
<li>EngieBackstory</li>
</spawnCategories>

<skillGains>
<li><defName>Crafting</defName><amount>4</amount></li>
<li><defName>Social</defName><amount>2</amount></li>
</skillGains>

<workDisables><li>Violent</li></workDisables>

</AlienRace.BackstoryDef>

@thegreyjester I did not do a single backstory for the lanius race i just released. They could use a hand :) I think i will still put your engie backstory in LTF.