[PS2, 2007] Negima!? Dream Tactic Yumemiru Otome Princess : DAT / GRP / MAP files extraction (Konami)

This is a strategy game by Konami (https://konami.fandom.com/wiki/Negima!%3F_Dream_Tactic_Yumemiru_Otome_Princess).

In the game's files, there seeems to be 3 types of files : DAT / GRP / MAP. DAT seems to be text files because opening these with Shift JIS gives the game's text. Images seems to be in these GRP / MAP files but I don't know how to extract (uncompress ?) these so feel free to help. 

Download link for the game's files (you can ignore the SOUND folder) : https://mega.nz/file/xJEWxD7b#yZk3NHjnVe63jNTpriLD6n2nV_x9xlXQhebzWE_OScI