Void Terrarium dev explains the practical reason for the game's Tamagotchi-style feature

In Void Terrarium, you are tasked with venturing out into dungeons to save the last human from a toxic work. That human, Toriko, has to live inside a terrarium to stay safe, but she can still face issues while you're out adventuring. You'll keep track of Toriko while out and about through a Tamagotchi-style system. In an interview with Siliconera, NIS’ Masayuki Furuya explains why such a presentation was chosen.

There are both negative and positive reasons for this. On the negative side, we wanted to have the player feel Toriko’s existence even while exploring the dungeons, but a 3D model or illustrations for it would have been an extra cost. So, we went for a relatively low-cost method. On the positive side, the O.S.E.Watch, as it’s called, has a very strong child-rearing feel to it and was popular around the office.