If you're looking for manga similar to FLCL, you might like these titles. All recommendations are made by Anime-Planet users like you!
20-something Meiko Otani is restless, living day to day with a job she hates and an unemployed boyfriend who'd rather be playing in a band. Like others her age, she struggles to find her place in the world and a purpose in life, so in an attempt to make a fresh start, she makes the decision to quit her job. Together with her friends, Meiko will embark on a journey of self discovery to find what will truly make her happy.
Both Solanin and FLCL revolve around the theme of 'growing up' and 'coming of age'. Both works display incredible artistry, and attention to detail. FLCL has much more fun and quirky characters, but Solanin's feel more realistic and grounded (I know, not saying much, but it's something).
If Haruko never showed up, FLCL would turn out exactly like River's Edge.
Both are coming-of-age stories set in a claustrophobic, industrialized town complete with looming factories and overgrown lots hemming a polluted river. Both have sketchy, messy-looking artwork, and a narrator whose jaded monologues about how boring life is contradict all the crazy/tragic turbulence of the plot.