'Asset bundles' refer to the files that the game uses to load assets at runtime. They are, as the name suggests, a collection of assets bundled together and compressed into a binary format. 'Assets' is a broad term that can refer to anything from models, to art, scripts, data files - essentially anything that is not in the main game binary.
They make up the bulk of the ~10GB install size of the game, and are downloaded on the initial download loading screen you are presented with after first installing the game, and whenever the game later prompts you to perform a data download.
On Android, if you have root access, you can see the asset bundles for your installation at the following path:
$ adb root
$ adb shell
$ cd /data/data/dev.dragaliafound.prod.game/files/assets
in which dev.dragaliafound.prod.game is the package name of the app generated by Dragalipatch.
Listing the files in that directory reveals buckets of files separated by the first two characters of each file name:
$ run-as dev.dragaliafound.prod.game ls /data/data/dev.dragaliafound.prod.game/files/assets
22 3F 4Q 63 7G AR C4 DH ES G5 HI IT K6 LJ MU O7 PK QV SA TL UW WB XM YX
23 3G 4R 64 7H AS C5 DI ET G6 HJ IU K7 LK MV OA PL QW SB TM UX WC XN YY
24 3H 4S 65 7I AT C6 DJ EU G7 HK IV KA LL MW OB PM QX SC TN UY WD XO YZ
25 3I 4T 66 7J AU C7 DK EV GA HL IW KB LM MX OC PN QY SD TO UZ WE XP Z2
26 3J 4U 67 7K AV CA DL EW GB HM IX KC LN MY OD PO QZ SE TP V2 WF XQ Z3
# ... and many more
The
run-ascommand is used to run the command as the package, so that you don't require root access to view the game's internal data directory. This allows you to perform asset modifications on a device that has not been rooted.
In each folder you will find the actual asset bundles:
$ run-as dev.dragaliafound.prod.game ls /data/data/dev.dragaliafound.prod.game/files/assets/DB
DB2F3CHPLCGVEST6MCCRTZUB7R3WQFF3ZQGSBXPXOXXVGBPW6J7A DBOQUH4EFZR2DGSCLYADO73IFDCLP3PQWVP5VGVV2OLUQMHBBEFA
DB3UL5MVQ3KWJUQYUI3ZZ5XFXPGKXQNB7442TEV2HQYQY46BGHBA DBOTOM5IMQJOZUNSGL5U6TPXCE7A4Z6YT6TGNBPK3P3DJR7TZ3TA
DB4NLG2E4VTBNRRODEXU7ZOWY72T5ZCRGSZEKB5AZLBXLNEWAEOA DBPUIXYJORBBUDVOJGS2XBT4PA6MRV3QMJSSKWK6RTHILLFAIFOQ
DB5B6W5KOU6T26HJF2ZSXYQYJVHVGZ6ZHFMV4UWNIDFQKJWBNAFQ DBQXZ7ZAOI2G53P3JKMCHG7DLGLQE655VBWZSXM22AK6C7BX7RTA
DB5M7WPC5FSBMTOHOKG7PJKNXB5ZJRNQOYU7EVAJFUB6I356EGCA DBRHHGSE75PT7IXVOEKT4HIL4D5LXZR4V6BGNE2PHGGQK4QCDNUQ
# ... and others
Each file name here is a truncated Base32 hash of the file contents.