skills marked with (?) means "not 100% sure of the description".
ATKアップ ATK +3 [ATKアップ+ gives ATK+8]
DEFアップ DEF+3 [DEFアップ+ gives DEF+8]
リベンジ The more the Stun gauge is full, the more damage your character deals.
サバイバー Increase health kit drop rate.
ドロップ+ Increase core drop rate [ドロップ++ Increases core drop rate greatly]
スナイパー Increase shot range.
スティンガー Pierce shots.
高速チャージ Increase charge speed.
自動チャージ Auto charge.
縄抜け名人 Easier to escape grapple (?)
強化+ Increased effect on item A (?)
回復+ Health kits heals more.
デュアルアップ ATK+5, DEF+5
経験+ Increase EN gain by 1.3x [経験++ Doubles EN gain]
隐れ上手 Increases the invisibility frame duration(?)
自然治療 HP regen.
This list may not be complete, those were just the ones I came across.