The reason why Tianhai Lantaro sacrificed voluntarily was his loyalty and dedication to brotherhood. In the novel "New Bullets Breaking V3", everyone kills each other in the new semester, Tianhai Lantaro is a gentle, caring, adventurous and emotional person. In order to realize the wishes of his friends and help them complete the ceremony of saying goodbye to this world, he died voluntarily. This reflects his strong spirit of sacrifice and dedication, and also shows his deep persistence in brotherhood.