Reel Robot Fishing is a side-game for Mobile Engagement Chassis, or optionally for any other mech rpg. It's also a viable standalone---about mech fishing.
The PDF is 2 pages, text only, but the information in it is organized in a way that makes it super easy to understand.
Gameplay is surprisingly crunchy, and character creation involves a number of moving parts. It also plays in real time, over the course of an hour.
To cast, you toss a d4 onto the provided board. Landing it in the right spots will give you an opportunity to try and reel in a fish, which is handled through a PbtA style 2d6 roll, which another player GMs.
If you fail to hook anything, you instead have a conversation with another player. Example topics are provided, and roleplaying fits extremely naturally into the context of the fishing excursion.
There are also a lot of excellent tips about building and maintaining atmosphere, including setting light level, ambient noise, and other elements.
Overall, if you're looking for a fishing game that plugs into any rpg, I strongly recommend this one. It holds up as a standalone, but it also really shines as downtime in a longer campaign. Definitely grab this if you have the chance.