A new key visual for the new Yu Yu Hakusho OVA announced at Jump Festa 2018 has been released and it details that the project will depict how Hiei and Kurama first met. The new OVA will be contained in the 25th Anniversary Blu-ray Box set for the series.
More details can be found on Studio Pierrot's official website for the box set's release:
http://pierrot.jp/yuhaku25/
Stay tuned to Anime Mojo for more details on the project as we look into confirming when the blu-ray box set will be released and whether region-free copies will be available for purchase.