If you liked the One Piece anime, the Anime-Planet community thinks you'd like:
Ippo Makunouchi is a loser. He has no friends, he spends his free time helping his mom with work, and he's constantly being beaten up by bullies. But that all changes when one day he's saved from another beating by Takamura, an up-and-coming boxer. Soon, Ippo turns his life around with a passion for the newly discovered sport, but his new lifestyle is far from easy! Before he can even dream of becoming champion, he'll have to overcome a slew of fierce rivals and learn what 'dedication' really means.
The future of humanity is in peril, as they are confronted with the threat of an intergalactic clash with a warrior-like alien race, and the only one who can save them is... Captain Tylor?! Join a crew of misfits and rejects including an alcoholic doctor, a gorgeous nurse, an anal-retentive commander and a bunch of really stupid marines as they try to make it out in space and to discover whether their captain is a misunderstood genius or a total moron like he seems to be.
Leadership is a very difficult thing. Someone says you can’t learn it but only gain from God. For Luffy and Tylor it's absolutely true. Main screen time they acting like fools without realizing what’s really going on, but when time comes they somehow managing to turn everything for their own benefit. Two desperate heaven-born captains definitely put these series together.
If One Piece’s length and Captain Tylor’s release date doesn’t scary you go ahead and watch them. You won’t be disappointed because a great comedy is a one more reason to unite these series.
Sumimura Yoshimori is a Kekkaishi – an inheritor of the power to battle demons, using barriers called kekkai. His family is charged with protecting the grounds of Karasumori high school, a building which magnifies the power of demons who enter it. Helping him are his spirit-wolf companion Madarao, and next door-neighbor Yukimura Tokine, the daughter of a rival clan. Years ago, Tokine was injured protecting Yoshimori, and now he is determined to become strong enough to keep her from being hurt again. Of course, he'd rather bake his exquisite cakes than have to fight demons at all, but fate has something else in store! As a shadowy demon organization moves to steal Karasumori's power, can Yoshimori overcome legions of demons, a centuries-old family rivalry, and a grandfather who just can't understand his love for baking?
Action, comedy, amazing characters. Each of these anime have this and more. Both Kakkaishi and One Piece drip with a large cast of enjoyable characters who will entertain you for hours. Fighting to protect the ones you love? They both address just that. If you like one you will like the other.
There's an adage that one man's trash is another man's treasure; but for Kosuke Ueki, one man's trash is another man's... tree?! Junior high school teacher Mr. K is in the running for the title of Celestial King. Candidates must select a junior high school student to endow powers upon, and then the students might fight each other mercilessly. The victorious student's benefactor will become the new Celestial King! Kosuke was Mr. K's choice, and for his power, he chose the ability to turn trash into trees. Furthermore, if he uses his abilities to harm others, he will lose one of his natural talents. Now, Kosuke must battle a variety of other power users to help Mr. K win it all, all while keeping his talents intact!
While at first glance these anime seem nothing alike, I couldn't help thinking of One Piece as a watched Law of Ueki. I think Ueki (the main character) reminded me of Luffy (the main character of One Piece.) Both of them punch before they think and ask questions latter. They also both gather a "crew" or "team" and make friends of their enemies. If you couldn't help but love one of these main characters, I would take a look at the other.
Keitaro Urashima is somewhat of a failure. In order to fulfill a promise he made to a girl fifteen years ago, he has tried time and again to get into Tokyo U but has never managed to pass the exam. However, fate smiles upon him and he ends up working for his aunt, managing an all-girls dorm! Living with the feral Kaolla, the timid Shinobu, the sake-loving Mitsune, the blade mistress Motoko and the punch-happy Naru, can Keitaro keep his focus and keep his promise? And will he ever end up meeting that girl from his past?