Recommended with flying stars! I'm not gonna get into the details, character or ideas as other reviewers did, instead I'll tell you about the technical parts. Undercurrent is a 1 volume - 11 chapters manga that's best read in one sitting. Toyoda sensei, as expected of him realistically portrays the daily life itself while slowly building up for the ending... And actually keeps you satisfied with the flawless execution of it. I was astonished with how he wrote the overall story. His panels resemble movie shots, something Fujimoto is praised for... While Toyoda sensei stays as a hidden gem... You could see how it would work asa hang-out movie like Sonatine.
Edit: This manga has been adopted into cinema as Undercurrent (2023)!

Unfortunately Toyoda sensei only wrote 2 full manga, which leaves us a bittersweet feeling for watching one of the greatest manga writers of our time quit without leaving much of a trace. He's around 60 now, I wish him a happy and healthy life going forward...