The OED has the following definition of in with examples underneath:
In the process of, in the act of; in case of: often equivalent in sense to a temporal clause introduced by when, while, if, in the event of.
- 1477 Earl Rivers (Caxton) Dictes 67 Gladdenesse, whiche encresses daily in me in lernynghe wysdom.
- ? a 1550 Life Fisher in F.'s Wks. (E.E.T.S.) II. p. liii, I am not affraid in gevinge you this counsell to take vpon my owne soul all the damage.
- 1591 Shakes. 1 Hen. VI, v. iii. 41 And may ye both be sodainly surpriz'd By bloudy hands, in sleeping on your beds.
- 1596 ― Merch. V. iii. ii. 320 In paying it, it is impossible I should liue.
- 1607 Stat. in Hist. Wakefield Gram. Sch. (1892) 58 Leaves word thereof att their howses in theire beinge abrode.
- 1846 MCulloch Acc. Brit. Empire (1854) II. 217 In estimating the chances which any candidate has of succeeding..no one ever thinks of inquiring into the politics of the tenants.
- 1864 Holme Lee In Silver Age (1866) 408 Kindness is not a quality that perishes in the using.
In is pretty much synonymous with in the process of in that sentence, carrying the meaning of contemporaneousness. The sentence says that when such a person is in the process of fulfilling their needs, they exhibit manipulativeness. It would be technically wrong to equate it with the statement that they use manipulativeness in order to fulfill their needs, although that can be its consequence, so most people wouldn't notice if you swapped in fulfilling with to fulfill in this case, I think.