Thank you so much for the 回層浮 translation! I have been brainstorming for ~2 hours, and honestly I think "Floating in Circles Through The Depths" is kinda perfect for the Kanji part! The "memories" part is already embedded in the　Reminiscence/回想 reading so I think it does not need to be repeated.

I really like the oxymoronic tension between "Floating" and "The Depths" which is also present in the lyrics with both 深層 (the depths) and 浮き輪 (life buoy), as well as 浮かんで　沈んで.

Also I think the choice of "through the depths" and not "in the depths" or "in the deep" is important as the latter two somehow paints just one "THE deep" monolith vs "through" which implies wading through layers.

The only alternative titles I can think of sound too much like "made-up" words, but I hope they can at least help in exploring ideas:

Floating through the Spiraling Depths
Spiraling, Floating through the Depths
Spiraling through the Buoyant Depths
Spiraling through the Depths of Buoyant memories
Spiraling through Deep Buoyant memories
Buoyant Spiraling through the Depths

"Spiraling" has a weaker implication of "Circling", but it's interesting to me since it can also contain/reinforce the "Floating/The Depths" contrast. It also kinda evokes a "Downward Spiral" which puts more rigor/speed to the movement through the layers, lightly referencing the 倍速で流れた日々 (days on fast forward) in the lyrics Other alternatives for "Circling" can be "Swirling/Whirling" (which are often associated with the movement of water/liquids) or "Orbiting" (which sounds too "Scientific", possibly may fit if the song was space-themed instead hahaha) "Buoyant" as an alternative for "Floating" can serve as a callback (err... callforward) to the Life Buoy/Life Ring in the lyrics. "Buoyant memories" is one of the most unfortunate "made-up" sounding phrases for me since it would fit greatly with "Reminisce", especially with the standard phrase 思い浮かぶ/"coming to mind"

As if this ask is not long enough, I would like to add:
- A search for "kaisou" in jisho.org also shows 快走 (fast moving/fast sailing) which kinda fits again with 倍速で流れた日々 but I'm not sure how commonly used that word is
- Apparently Penguins and Whale Sharks (Both featured in Tomori Band-aids!) often swim in circles. It is very unlikely, but I wonder if this was a consideration for the 回, especially since circles/circling was also very prominent in the MV https://news.mongabay.com/2021/03/from-penguins-to-sharks-to-whales-swimming-in-circles-is-a-surprisingly-common-trait/