Nega-kun and Posi-chan - Vol. 4 Ch. 42 - Against Big Brother

[MangaDex]

 

[Xalphire]

Brother approved(?)

 

[Cynn]

He scowled, he smiled, he beheaded a doll but also took his shoes off when he entered the room. This future brother in law is a terrifying blend but Nega made his impact.

 

[stonks4251]

He may be negative but he's got backbone

 

[Magnus_Prime]

Huh... The expression of the older brother in the second-to-last panel reminds me of what's-his-name from 'Kuzumi-kun...'