Watching the news, Takemichi Hanagaki learns that his girlfriend from way back in middle school, Hinata Tachibana, has died. The only girlfriend he ever had was just killed by a villainous group known as the Tokyo Manji Gang. He lives in a crappy apartment with thin walls, and his six-years-younger boss treats him like an idiot. Plus, he’s a complete and total virgin… At the height of his rock-bottom life, he suddenly time-leaps 12 years back to his middle school days!! To save Hinata, and change the life he spent running away, hopeless part-timer Takemichi must aim for the top of Kanto’s most sinister delinquent gang!!

Source: Kodansha Comics, Vol. 1

Notes:

• The original Japanese title contains the manji symbol, so it will not be removed from the title on MangaDex.
• Addendum on the "Manji" for those uninformed. From Seven Seas' Omnibus Edition:
  "In East Asia the manji (卍) is an ancient religious symbol of power and good fortune for many different countries and religions around the world, including Buddhism, Hinduism, Jainism, and a number of Indo-European and Native American religions as well."
  "The specific meaning of the symbol varies by nation and religion, and also by the position of the "arms" of the cross--whether they face left or right, or whether the cross is tilted or straight."
  "In the 1930s, the swastika symbol--a clockwise, tilted cross--was adopted by the Nazi Political Party in Germany, and gained a negative reputation as a symbol of hatred in the modern world."
  "The manji used by the Tokyo Manji Gang as their emblem is intended to be the ancient Buddhist symbol, as evidenced by the appearance of its counterclockwise, straight arms..."

Links:

• Official English Translation (Seven Seas)
• Official English Translation (Kodansha USA)