PSP game Tsugi no Giseisha o Oshirase Shimasu Houkaisuru Sekai ni Shinigami to

[Monokuma77]

Hi, I'm trying to find the text for the Japanese PSP game Tsugi no Giseisha o Oshirase Shimasu Houkaisuru Sekai ni Shinigami to. I'm kinda new to this, so I would like some help.
The format seems somewhat standard and is similar to Gakuen Hetalia PSP.

In the USRDIR I have 4 files. Data.Dat, STS.DAT, STS.MAO, STS_DEF.TOB
STS.DAT has a PSPFS_V1 header so I can unpack it with quickbms.
The unpacked files are dat, vag, sp2, mbp, at3,  bin.
.vag are known audio files,
.at3 are modified wav files,
.sp2 are modified tga files,
.mbp are definitely image files,
.bin files are very very small
Now the dat files are modified gzip files which I can unpack but they seem to contain more of the same files, that is mbp, sp2 etc.

So where is the text? What am I missing here?

[tryphon]

Some of it must be in the executable (SYSDIR/BOOT.BIN). Be careful, BOOT.BIN is surely compressed / encoded. If there's an EBOOT.BIN, it may be (or not) the decompressed version of the BOOT.BIN. You can then delete BOOT.BIN and rename EBOOT.BIN as BOOT.BIN

Text itself is surely encoded. You may find the table in the executable, or among the graphics files. This way, if you figure out how the text is encoded, it'll be simpler to find text files if any (I don't know if there's lots of texts in this game ; maybe everything is in the executable), assuming it's encoded the same way.