Tag! (Fallout Supplement)
From D&D Wiki
You've focused on a skill so long, you gain full insight into it that others of your class wouldn't have seen otherwise.
Prerequisite: Level 3, Intelligence 12.
Benefit: You can make any one cross-class skill into a class skill. This increases the rank by +1 for each rank already spent on the skill.
Special: You can take this feat as many times as you like.