The 22-year-old, who signed on a free transfer last summer, had been a revelation in the absence of Joseph Mills before suffering a hamstring injury against Stevenage three weeks ago.
However, he replaced Mills for the final 20 minutes against Bradford and now wants to win back his place as Jon Brady’s first-choice left-back for the final five games of the season.
"It felt really good to be back,” said Koiki. “I’ve recovered from the injury pretty well and I’m just getting back into things.
"I was confident in my recovery. Obviously I didn’t play 90 minutes at the weekend but it was nice to come off the bench and get back on the pitch.
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"That gave me a chance to test it out and see how I felt and I’ve pulled up well so that’s good.”
Koiki has enjoyed a hugely impressive first season at Sixfields, so much so the club were quick to trigger a clause in his contract which extended his stay at Sixfields by another 12 months.
The former Burnley and Crystal Palace youngster started 29 games in a row between September and March and was linked to big-hitters Sunderland and Sheffield Wednesday during the January transfer window.
But he doesn’t want to rest on his laurels and intends to make sure he finishes the season as strongly as he started it.
He added: "I have played a lot of games this season, more than before, but I feel by body has come through quite well.
"I started a lot of games in a row when Millsy was out and that was really good for me because it’s important to have that repetition and get into the groove of things and play consistently.
“I’m really pleased with how the season has gone but it’s not over yet. We still have five games to go and all that matters is what happens at the end of the season and where we finish.
"Obviously I’m happy with my progress because I’ve got games under my belt and I feel I have showed what I can do but I need to keep striving and make sure I finish the season strong.”
Cobblers are fifth in Sky Bet League Two and still believe automatic promotion is a possibility this season, but they also have work to do to secure a play-off place.
Much will hinge on this weekend’s Easter double-header, with a trip to Oldham Athletic first up tomorrow (Friday) before Harrogate Town visit Sixfields next Monday.
"It’s an important weekend with it being two games back-to-back,” Koiki continued. “It’s a quick turnaround for us and we want to build momentum from the first game to take into the second game.
"It’s very tight up there and we are still striving for promotion so every game matters now – we don’t have much margin for error.
"We expect a tough game against Oldham. They will look to come out of the blocks fast but we are ready to fight.”