There are plenty of special edition Skyline GT-Rs around from various tuning houses like Mine's and Nismo. And here's one from HKS that is quite rare..

Dubbed the Skyline R32 HKS Zero-R, this 90s car is said to be one of the rarest Skyline ever built and is one of the four original units HKS built at first. The company was wanted to send the car to be homolgated for sale but rules back then required the HKS to crash test a number of cars to register them as one-off models. Costing more than S$150,000 each, the Zero-R was too much to be crashed, forcing HKS to abandon the project with only four units built.

The car shown here lives in Brunei currently and used to belong to the Sultan of Brunei. The rest of them are supposedly still in Japan.

Interestingly, HKS built another few units of Zero-Rs after the government relaxed its rules in 2005 but these six are not as sought as after as the original batch of them.

https://www.youtube.com/watch?time_continue=27&v=bqcGpMqxjxQ