Trigger Keeper (トリガーキーパー, Torigā kīpā) is a two-part one-shot created by Daisuke Ashihara. It is the first precursor to the World Trigger manga series.
(from the World Trigger wiki)

Yukimaru and his friends investigate the Shiroyashiki as they look for their missing friends and run into the strange Room 303.

4 koma anthology
ASHIHARA Daisuke
ASO Shuuichi
KAITO
KOMI Naoshi
KUBO Tite
NUMA Shun
ODA Eiichiro
SHIMABUKURO Mitsutoshi
SORACHI Hideaki
TABATA Yuuki

Creatures from another dimension have invaded Earth! Earth weapons are useless against these "Neighbors", but some scientists have created new weapons based on the enemy's technology. Using these weapons, humans struggle to defend themselves from the invaders.

The head of the central base has sent the ace soldier, Yuuichi Jin, to help out the failing Base 7, and rescue his son Yuiga Tadashi, who is the leader there. Unfortunately, the problem with Base 7 is, in fact, Yuiga Tadashi. He's a terrible leader who cares for nothing but his own reputation and believes that being the central base leader's son allows him to do whatever he wants. Will Jin be able to fix this terrible situation?

Talented Elite Jin is a oneshot created by ASHIHARA Daisuke. It is the second precursor to the World Trigger manga series, the first of which is Trigger Keeper.

From Artificial Demons:

In the series, the Hino family picks up their "little brother" from the airport. The "brother" turns out to be Rilienthal, an intelligent dog who speaks Japanese. He is also the target of men in black suit from a mysterious organization. They refer him as RD-1.

A gate to another dimension has burst open, and from it emerge gigantic, invincible creatures that threaten all of humanity. Earth's only defense is a mysterious group of warriors who have co-opted the alien technology in order to fight back!