
waaaaait where's the manga w/ the other couple?

https://www.mangaupdates.com/series.html?id=114432
No one has done it yet.

is this seriously a harem? can't eru just be excited about his robots???

There is no harem, despite what you might believe. The only thing the MC is interested in is robots and blowing sh*t up. 4 LN in, and 4 in story years later, not a sign of romance in sight.

Correction, 5 LN vols in ( I just finished reading vol. 5), and there is still not a sign of romance for the MC. His childhood friend is getting some action though.
the last panel lmao http://www.mangago.zone/read-manga/sasaki_to_miyano/nbt/f41919ef8372dd54640becdc667c1bb4_chapter-4/pg-10/