The story of Mix takes place in the same Meisei Gakuen high school as Touch, only it is set 26 years later. Like Touch, Mix revolves around brothers and baseball as a main theme.
(Source: ANN)

Kitamura Koh has known the Tsukishima family for years. One of the Tsukishima daughters was even born on the exact same date as Koh! What will become of Koh when his best friend is no longer around?

(Summary from here):

Wakamatsu Masato lives with his step-sister, Miyuki, whom he does not have blood relationship with. Their father is always working oversea (in fact, he has not appeared in the manga at all...) and left the two of them living by themselves in Toukyou. Miyuki is cute, nice, sensitive and very popular among guys around Masato. Masato has a girlfriend at school whose name is Kajima Miyuki, who is pretty and gentle, the ideal dream of every high school boy. It took years for Masato and his sister to realize whom they love and care most after a lot of events. The manga is very nicely written, with excellent layout, interesting story and character developments, refreshing art style and filled with youth and emotion. It also shows the dramatic improvement of the author's skill.

Minori is the manager of her high school's baseball club, which has been defunct up until five years ago. Even now, it's a little rough, since there currently are no seniors in the club at all! None of the second year players know why the club closed so many years ago, or about the baseball history all their fathers share...

Satomi Azusa is a popular teenage gravure idol. She's also a highly talented baseball player, but, as a girl, she can't play on her school's team. Her father happens to be the coach of the team, and he concocts a scheme to allow her to play. His scheme involves Hirayama Keita, Azusa's childhood friend, a teenager of no particular talent. Keita's redeeming feature is that he looks a lot like Azusa. In fact, after putting Keita in a wig and girl's clothes, not even their parents can tell the two of them apart. To help Azusa's (and her father's) dream come true, Keita agrees to trade places with her during the baseball games. Soon "Hirayama Keita" becomes a popular player, and "he" begins to move towards a career in pro baseball. How long can Keita and Azusa keep up the act? What will happen when people find out?
(Source: MangaHelpers)

Jinbe a fromer soccer goalkeeper is now an aqaurium technititan, has a stepdaughter.
Jibe's wife passed away.
His stepdaughter doesn't yet know how much she loves him or what Jinbe's feelings are for her?

Will this relationship turn into something more than stepfather and stepdaughter?

Yamato Keisuke, a promising freestyle swimmer, and Ninomiya Ami, a talented diver, are the offspring of two rival families owners of confectionery shops. Two generations ago, Grandfather Ninomiya came up with an idea for an owl-shaped cake, but Grandfather Yamato quickly raised to the challenge and thought of a similar cake--but in Yamato's the owl had ears. Because they're priced the same, Yamato's extra ears were crucial, and that made the business of the Ninomiya confectionery suffered. Grandfather Ninomiya then fell ill worrying about his shop. Before his death, his last words were "I was killed by the Yamatos", and since that moment the two families have been sworn rivals.
(Source: MU)

From AnimeNfo:

Kunimi Hiro and his best friend Hideo were baseball wonders... Until Hiro found out his arm was permanently damaged, rendering him unable to play anymore. A frustrated Hiro goes through the trouble of specifically finding a high school with no baseball team... Only to later on find out the doctor who examined him was a quack and his arm is perfectly fine. Hiro is quick to reinstate his dream: Creating a baseball team for his school and getting to face off against Hideo in the Koshien... The number one premier league for high school baseball.

Track and field star Nimi, sees a boy molesting a girl on a train and he falls in love with her at first sight, as he get off the train he watches a baseball game where the girl is crying, her father is the coach of the team and the team is losing badly, he then swear to join the baseball team to make her happy, but there are obstacles one of her childhood friends is a extremely talented baseball player and loves her, and is always proposing to her and trying to make her his, and then there is another girl the ace of the track and field team who has fallen in love with Nimi when he was still doing track and field, and is trying to make him hers.

15 year old Kasumi Kishimoto arranged to stay with her aunt when she entered high school. Upon ariving she is surprised to learn that there are four other people boarding there, all of whom are male and attending the same high school. And when one of them walks in on her bathing on her first night there, she wonders what she's gotten herself into.

[From Mangascreener]:

The only common feature running through these stories is a grown-up protagonist somehow coming face-to-face with his childhood past, in a testament to the loss of youth, the disillusionment of growing old, and nostalgia for better times. In the Adachi pantheon, this is a rare diametric view of his eternal theme of "youth," in this case youth as seen through the lens of the past. It's a powerful statement from Adachi that might even be an acknowledgment of his steadily-creeping age. What is impressive about these stories is not the plots or characters themselves, but the absolutely perfect way he tells them, another facet of experience that comes with age. Most of the stories may require multiple readings to fully appreciate the airtightness of the plot and visual motifs."

Enter our hero Wakadaishou! He doesn't have much interest in school; he saves his energy for all the excitement he can stir up after school. This is an early Adachi Mitsuru 'youth manga', filled with engaging characters, comic scenes, and a young hero with a zest for life.

15-year-old Atsushi Ando moves back to his home town with his family after 6 years. The story focuses on the fortunes and misfortunes he encounters in this town mostly due to pranks pulled by the ghost of his older brother Hitsushi Ando, AKA Q-Chan, whose death prompted the family to move away. The catch is that only Atsushi can see his brother's ghost.

Collections of short stories:
Volume #1:

Volume #2:

Volume #3:
-Ace of hearts
-Teens
-Wind and Leaves
-Hirahira's stories

Volume #4:

Hirahira-kun is a boy that likes helping the most weak, and for that he uses his creativity to think up plans to defeat his corrupted senpais and so to maintain the entirety of his colleagues of class.

This collection, titled simply Short Program, collected stories by Adachi published between 1985 and now.

Volume 1:
Story 1 - Change
Story 2 - Take Off
Story 3 - Short Program
Story 4 - What's Going On!? (Part 1)
Story 5 - What's Going On!? (Part 2)
Story 6 - At the Intersection
Story 7 - The Current State of Affairs
Story 8 - Plus 1
Story 9 - Purple

Volume 3:
Story 1 - Clogs and Diamond
Story 2 - Where the Wind Blows
Story 3 - Angel's Hammer
Story 4 - Memory Off (Pt. 1 & 2)

Sports comedy with psychic powers. The story revolves around six children and a cat who save a religious icon from a fire, in reward for which the temple god grants each of them a power that will activate on their 13th birthday. Upon entering junior high school together, the six are forced to join the Sports Rental Club, which provides temporary members to other clubs when the regular members can't participate. The main character is Misora, a straight forward type of girl who likes physical activities like kickboxing.
(Source: Wikipedia)