Saw this uploaded on Kiyoshi Sakai's youtube channel. It looks like he had finalized the character design but was looking for a good game idea to go with it.
https://www.youtube.com/watch?v=tBCWAJnSn3E
There's a translation for the video here:
https://twitter.com/necrosofty/status/1064961668873052160?s=19
About seven tweets starting from the link above explaining the video.
Sakai posted footage of an x68000 prototype of Umihara Kawase with the rubber fishing line mechanic we all know and love.
https://www.youtube.com/watch?v=w27cnNOZhkg
https://www.youtube.com/watch?v=aFcC571x5zM
Those placeholder textures for everything feel familiar, its exciting seeing levels I recognize. I dislike how slow the enemies are now but I see with respawning enemies it is really hectic when faster. And are those the puff textures on release too? This looks far more like the game we got and I love it, it was solid from such an early state
I find it really interesting to see what games looked like during planning and development, seeing how much changed and what didn't change. It's pretty cool to see the completely different early concepts for Umihara Kawase and how that process led to the idea of swinging around and attacking enemies with a fishing line. As Canvas noted, the fishing line prototype's textures have a familiar feel, and the prototype even has a familiar level -- the prototype's Test Stage 3 becoming the final game's Field 10. I definitely agree that the enemies' speed makes it look pretty hectic and I'm glad that was changed for the final release. It does make me wonder, though, what the final game would be like to play with faster enemies (but without the respawning!)