Playing second-division football just over a year ago, Fullkrug helped Bremen to promotion before winning a first Germany cap at the age of 29, foreshadowing a move to Signal Iduna Park before the transfer window closed in August.
Fullkrug will suit up for Dortmund just 48 hours after the club chartered a private jet to bring the striker, along with midfielder Julian Brandt and defenders Mats Hummels and Niklas Sule back from Germany's US tour.
The reported 100,000 euro (£87,200) cost for the flight will be worth it if Dortmund, who currently sit fourth, pick up three points and go top of the table - for one night at least.
With Sebastien Haller struggling for form as he continues his comeback from testicular cancer and Youssoufa Moukoko ruled out of Friday's match with injury, the 30-year-old has become an indispensable part of Dortmund's front line.
Fullkrug has adjusted well to the bright lights in Dortmund and has scored in each of his past four games for club and country.
"Niclas has fit in very well," Dortmund coach Edin Terzic said on Thursday. "You can see what a positive person he is."
"He has helped us a lot with his quality and his activity."
Fullkrug made his senior debut for Bremen's second team at the age of 18 before moving to the first team. The forward then bounced around German football for the best part of a decade, before returning to Bremen in 2019, with persistent knee injuries preventing Fullkrug from reaching his potential.
The striker shared the Bundesliga top scorer trophy last season and has had a successful international career, with nine goals in 11 matches for Germany.
Despite Fullkrug's hasty exit, there is no bad blood between the two, with Bremen sporting director Frank Baumann admitting the striker's sale helped balance the books and avoid an equity injection for the cash-strapped club.
"The economic necessity was too great," Baumann told Sky Sports in September.
Bremen coach Ole Werner said on Wednesday he was looking forward to "an absolute highlight of a game" - and to seeing his former striker.
"For me, it doesn't matter in my everyday work to see him on the other side."
Looking forward to the clash after his transfer in September, Fullkrug said "this will be one of the most special games of my career".
Despite the move, Fullkrug continues to hold his old side dear, TV cameras revealing he still plays in green and white Bremen-branded shin pads for his new side.
The striker told Germany's Sky Sport in September the shin pads "still work well", saying "I scored plenty of goals with them and had lots of success."
"They're special, they fit, they're good, and other than that, Werder is also a team I still really like a lot."
One to watch: Harry Kane (Bayern Munich)
England captain Harry Kane's eight goals in seven league matches has shown his importance up front for Bayern Munich.
Kane's Bayern travel to Mainz on Saturday, where they have lost three of their past five matches.
Should Xabi Alonso's unbeaten Bayer Leverkusen win at Wolfsburg earlier on Saturday, Bayern will come into the game five points behind them - putting pressure on Thomas Tuchel's undermanned side to keep pace.
Kane scored twice in England's come-from-behind 3-1 win over Italy on Tuesday and now has more Wembley goals than any other England player.
While Kane said he was "proud" to overtake Bobby Charlton's record at England's home of football, he said "but you know me, it's always about the next challenge".
Key stats
13: Bundesliga top scorer Serhou Guirassy has 13 goals in seven games — two more than the striker had in the entirety of last season.
Three in six: Last season, Werder Bremen scored three goals in the final six minutes away at Borussia Dortmund to turn an 89th-minute 2-0 deficit into a 3-2 victory.
Three: Dortmund, Leverkusen and Bayern are the only unbeaten teams remaining in the league.
Fixtures (2.30pm BST unless stated)
Friday
Borussia Dortmund v Werder Bremen (7.30pm)
Saturday
Wolfsburg v Bayer Leverkusen, Darmstadt v RB Leipzig, Union Berlin v Stuttgart, Hoffenheim v Eintracht Frankfurt, Freiburg v Bochum, Mainz v Bayern Munich (5.30pm)
Sunday
Cologne v Borussia Monchengladbach (2.30pm), Heidenheim v Augsburg (4.30pm)
