Nerdcore Techno is not to be confused with Nerdcore Hip Hop. It is coincidental that these were named similarly.
Nerdcore Techno is a style of electronic music that emerged in Japan in the early 90's and was popularized by labels such as 全日本レコード and Toy Label as well as Jungle/Techno collective サイケアウツ. It is most often seen as a combination of Techno, Breakbeat and Jungle, known for remixing melodies/heavy sampling of typical Japanese (and occassionally western) pop culture and incorporating a comedic and/or nostalgic undertone. Often referencing either campy 80's and 90's pop culture or otaku/nerd culture such as anime or videogames, there is some overlap with J-Core artists/labels, and Nerdcore Techno can be seen as the foundation of J-Core. But while J-Core focuses on the Hardcore side of things, Nerdcore Techno focuses on the Techno and Jungle side of music. The BPM can vary a lot depending on the artist's personal style but it often ranges between 130 and 160 BPM, leaning towards the higher BPMs and can sometimes go as high as 180 BPM.
Nerdcore Techno's origins seem to draw inspiration from early techno acts like Yellow Magic Orchestra and Kraftwerk. One of the earliest known examples of what could be reasonably be considered nerdcore is a track called サイバー長介 by 猛毒 (https://youtu.be/q7440o6YTkk), released in 1992.
Many underground events focused on Nerdcore Techno were held and articles appeared on Nerdcore Techno during the 90's in Quick Japan, a prolific music magazine. At the peak of its popularity it had a significant following in Japan, though it remains largely an unseen, fleeting and mysterious movement outside of Japan. Today, Nerdcore Techno continues to live on mostly on the internet in the form of netlabels such as Anything Records, but there are still examples of labels that organize parties and release (pressed) physical releases. Toy Label (among others) still regularly releases physical albums, and overseas it has gained some traction as well in the form of labels such as NiTEFLARE and Allkore.