Total Recommendations: 3
Both animes about a character that has extremely good skill for their age/who they are. Princess Nine deals with a female girl with very good skill, while Prince of Tennis deals with a young bot with extremely good skill.
Both deal with aliens being that Gantz deal with it a little bit more. Also both may have you wondering what the hell is going on and why. Gantz has a lot of blood and gore like higurashi, just that Gantz has way more, well higurashi deals with more mystery than Gantz.