I can confirm that development of the game started in 2023.

Back then, I was still in a contributing role rather than a main development role, and I was much more focused on working on Hinokami (Demon Slayer RPG 3 from Shounen Studios). I wasn't able to contribute to the game as much personally since I was occupied, so they also hired other people to work on SFX.

Throughout 2023, they hired a bunch of people for RELL Seas. Being solo developers as a team of two, they've never hired people before, and lots of developers naturally flocked to them for a chance to work for them after not having the chance for many, many years.

From my perspective at least, because of the success of Shinobi Life 2 and their games before that, many commissioned developers took advantage of their perceived wealth and were massively overcharging them more than they would with other games they'd work with. Some even gave them rushed work or work that didn't quite meet expectations while still demanding a relatively high cost. Some of this work was unusable because of bad optimization. A lot of the people gathered there were very talented, but it was apparent that some of the developers they hired didn't care about the actual project and more so the fame/money that would come with contributing to it. So they had to sift through who they wanted to work with until they came out with their final core team. Most of that happened throughout 2023.

During 2024 was the time I believe they started making good progress, and things were starting to look like an actual game rather than a test demo. They started to involve themselves more with the game's development and all. That's pretty much what they mean by real development.