Mahachi scored 13 goals in 79 appearances across three seasons with the Durban-based outfit.
When it comes to players moving from Arrows to Pirates, the 24-year-old is following in the footsteps of the late Bheka Phakathi, Njabulo Manqana, Siyabonga Sangweni, Thamsanqa Gabuza and most recently Thembela Sikhakhane.
Striker Chideu scored twice in seven outings in 2017/18, having only linked up with Abafana Bes'thende in October last year following a spell at Ajax Cape Town.
"Thomas Chideu has been released and Kuda Mahachi is leaving to Orlando Pirates, like we all know," Larsen tells KickOff.com.
Larsen, who represented Pirates in his younger days, admits it will be tough to replace playmaker Mahachi.
"It's always hard to lose a quality player like that, I rate him very highly," Larsen says of the ex-Mamelodi Sundowns man.
"We had a very good working relationship. He really performed well for the club and we are going to miss him but life goes on ... this is the nature of football. We'll continue to fight without him."
Larsen adds: "We are in the process of looking at bringing players in to strengthen the team, but as Arrows usually do, we look within the team first.
"We'll be looking at the MultiChoice Diski team first and maybe the solution is here in front of us, so that's what we'll be doing."