The PSP never received a direct port of MapleStory—its library leans toward single-player experiences rather than 2D side-scrolling MMORPGs. However, several titles capture the anime aesthetic, grind-heavy progression, or side-scrolling action that define MapleStory's charm.
If you want MapleStory on the go, play MapleStory M (iOS/Android)—the official mobile adaptation. For PSP hardware, consider remote play (PS3/PC → PSP) or homebrew (PPSSPP on phone) to stream the PC version.
Bottom line: PSP excels at single-player RPGs with depth. Monster Hunter and Tactics Ogre (also on PSP) are the closest "grind & grow" experiences.