Opener Villani, who took over the Rockets captaincy to allow Nat Sciver to focus on her batting and bowling roles, made her total off 40 balls as the Rockets overhauled a modest 100 for eight with 18 balls to spare.
Villani shared an unbroken match-winning partnership of 64 with South Africa's Mignon du Preez, whose 32 from 20 balls included back-to-back boundaries off New Zealand's Annabel Sutherland to win the contest.
Australia international Nicola Carey top-scored with 27 off 29 balls, with Sarah Bryce making 23 off 26, as the Welsh side struggled for fluency on a used pitch.
Rockets were excellent in the field, Villani holding two good catches, Bryony Smith taking an excellent one and Du Preez pulling off a four-saving dive at deep cover.
Their bowlers gave little away, with leg-spinner Alana King going for just 10 runs from 20 deliveries.
Fire captain Tammy Beaumont opted to bat first and launched the innings with four consecutive fours off Kathryn Bryce.
But that was as good as it got for her team, who found the boundary only five more times, with three coming in the final nine deliveries as Carey and Lauren Filer finally threw off the shackles.
England opener Beaumont miscued a ball from off-spinner Smith at the start of the second set, with Sarah Bryce gaining an element of revenge by taking the catch at cover.
Kathrine Brunt conceded just seven runs in back-to-back sets while Sciver dismissed Australian duo Rachael Haynes and Sutherland in the space of five deliveries as Fire closed the powerplay on 31 for three.
Opener Sarah Bryce - Kathryn's younger sister and fellow Scotland international - hung around doggedly but it was an anchor role for which only Carey provided any meaningful support, the pair adding 33 off as many balls for the fifth wicket before Bryce was run out by the bowler chasing a single off Georgia Davis.
After a sedate start lifted only by Villani pulling Sutherland for six over the head of deep backward square, Rockets were 25 without loss after 25 balls, behind on the powerplay comparison but up with the required rate.
They soon lost Smith, caught at deep midwicket, and Sciver failed to cash in after being dropped early on as she was caught at short third when reverse sweeping Alex Hartley.
But Villani took three fours in five balls off Carey and survived a difficult chance to deep backward square on 46.
Du Preez chipped in with six over midwicket off Hartley as the duo eased their side to victory.