We know from PSIV that the heroes of Algo are called "Protectors" and their spirits go to Esper Mansion and Elsydeon after they die. But, what do you think qualifies someone to become one of these protectors?
When Chaz sees the spirits or memories in PSIV, he sees all the heroes of PSI and PSII. These are the people that fought the great evils of their time and saved their worlds - except for two cases. One is Nei, who didn't know anything about Dark Force or fight Mother Brain. Another is Nero, Alis' brother, who took action before his sister, even if he didn't get as far. But Nei is there and Nero is not... why do you think that is? Why was Nero excluded?